libmm-glib,common-helpers: make hexstr2bin() return a guint8 array

It makes much more sense than returning a gchar array, as gchar is
signed.

libmm-glib/mm-common-helpers.c

@@ -1686,18 +1686,18 @@ mm_utils_hex2byte (const gchar *hex)
     return (a << 4) | b;
 }
 
-gchar *
+guint8 *
 mm_utils_hexstr2bin (const gchar  *hex,
                      gssize        len,
                      gsize        *out_len,
                      GError      **error)
 {
     const gchar *ipos = hex;
-    g_autofree gchar *buf = NULL;
+    g_autofree guint8 *buf = NULL;
     gsize i;
     gint a;
-    gchar *opos
-;
+    guint8 *opos;
+
     if (len < 0)
         len = strlen (hex);
 
@@ -1723,7 +1723,7 @@ mm_utils_hexstr2bin (const gchar  *hex,
                          ipos[0], ipos[1]);
             return NULL;
         }
-        *opos++ = a;
+        *opos++ = (guint8)a;
         ipos += 2;
     }
     *out_len = len / 2;

libmm-glib/mm-common-helpers.h

@@ -181,7 +181,7 @@ gchar    *mm_get_string_unquoted_from_match_info (GMatchInfo  *match_info,
 const gchar *mm_sms_delivery_state_get_string_extended (guint delivery_state);
 
 gint      mm_utils_hex2byte   (const gchar *hex);
-gchar    *mm_utils_hexstr2bin (const gchar *hex, gssize len, gsize *out_len, GError **error);
+guint8   *mm_utils_hexstr2bin (const gchar *hex, gssize len, gsize *out_len, GError **error);
 gchar    *mm_utils_bin2hexstr (const guint8 *bin, gsize len);
 gboolean  mm_utils_ishexstr   (const gchar *hex);