port-serial-at: make mm_port_serial_at_command_finish() transfer ownership

This will make it slightly easier to port mm_port_serial_at_command() to
use GTask, since we won't have to keep a pointer to the result in GTask
after _finish() has been called.

In most cases the caller needs the value anyway, so this doesn't add too
much hasle.

src/plugins/cinterion/mm-plugin-cinterion.c

@@ -80,7 +80,7 @@ sqport_ready (MMPortSerialAt *port,
               GTask          *task)
 {
     MMPortProbe *probe;
-    const gchar *response;
+    g_autofree gchar *response = NULL;
 
     probe = g_task_get_source_object (task);
 

src/plugins/dell/mm-plugin-dell.c

@@ -158,7 +158,7 @@ response_ready (MMPortSerialAt *port,
 {
     CustomInitContext *ctx;
     MMPortProbe       *probe;
-    const gchar       *response;
+    g_autofree gchar  *response = NULL;
     GError            *error = NULL;
     gchar             *lower;
     DellManufacturer   manufacturer;

src/plugins/huawei/mm-plugin-huawei.c

@@ -104,7 +104,7 @@ getportmode_ready (MMPortSerialAt *port,
     MMDevice                *device;
     MMPortProbe             *probe;
     HuaweiCustomInitContext *ctx;
-    const gchar             *response;
+    g_autofree gchar        *response = NULL;
     GArray                  *modes;
     g_autoptr(GError)        error = NULL;
 

src/plugins/longcheer/mm-plugin-longcheer.c

@@ -61,7 +61,7 @@ gmr_ready (MMPortSerialAt *port,
 {
     MMPortProbe *probe;
     const gchar *p;
-    const gchar *response;
+    g_autofree gchar *response = NULL;
 
     probe = g_task_get_source_object (task);
 

src/plugins/novatel/mm-common-novatel.c

@@ -49,10 +49,11 @@ nwdmat_ready (MMPortSerialAt *port,
 {
     g_autoptr(GError)  error = NULL;
     MMPortProbe       *probe;
+    g_autofree gchar  *response = NULL;
 
     probe = g_task_get_source_object (task);
 
-    mm_port_serial_at_command_finish (port, res, &error);
+    response = mm_port_serial_at_command_finish (port, res, &error);
     if (error) {
         if (g_error_matches (error, MM_SERIAL_ERROR, MM_SERIAL_ERROR_RESPONSE_TIMEOUT)) {
             custom_init_step (task);

src/plugins/sierra/mm-common-sierra.c

@@ -105,7 +105,7 @@ gcap_ready (MMPortSerialAt *port,
 {
     MMPortProbe *probe;
     SierraCustomInitContext *ctx;
-    const gchar *response;
+    g_autofree gchar *response = NULL;
     GError *error = NULL;
 
     probe = g_task_get_source_object (task);

src/plugins/telit/mm-common-telit.c

@@ -185,7 +185,7 @@ getportcfg_ready (MMPortSerialAt *port,
                   GAsyncResult *res,
                   GTask *task)
 {
-    const gchar *response;
+    g_autofree gchar *response = NULL;
     GError *error = NULL;
     MMPortProbe *probe;
     TelitCustomInitContext *ctx;

src/plugins/ublox/mm-plugin-ublox.c

@@ -151,10 +151,11 @@ quick_at_ready (MMPortSerialAt *port,
 {
     MMPortProbe       *probe;
     g_autoptr(GError)  error = NULL;
+    g_autofree gchar  *response = NULL;
 
     probe = g_task_get_source_object (task);
 
-    mm_port_serial_at_command_finish (port, res, &error);
+    response = mm_port_serial_at_command_finish (port, res, &error);
     if (error) {
         /* On a timeout error, wait for READY URC */
         if (g_error_matches (error, MM_SERIAL_ERROR, MM_SERIAL_ERROR_RESPONSE_TIMEOUT)) {

src/plugins/x22x/mm-plugin-x22x.c

@@ -63,10 +63,10 @@ gmr_ready (MMPortSerialAt *port,
            GAsyncResult   *res,
            GTask          *task)
 {
-    MMPortProbe *probe;
-    const gchar *p;
-    const gchar *response;
-    GError      *error = NULL;
+    MMPortProbe      *probe;
+    const gchar      *p;
+    g_autofree gchar *response = NULL;
+    GError           *error = NULL;
 
     probe = g_task_get_source_object (task);