core: fix loop limits in echo removal

-1 was actually correct, if data->len is 10, i goes from 0 to 8.

src/mm-at-serial-port.c

@@ -66,7 +66,7 @@ mm_at_serial_port_remove_echo (GByteArray *response)
     if (response->len <= 2)
         return;
 
-    for (i = 0; i < (response->len - 2); i++) {
+    for (i = 0; i < (response->len - 1); i++) {
         /* If there is any content before the first
          * <CR><LF>, assume it's echo or garbage, and skip it */
         if (response->data[i] == '\r' && response->data[i + 1] == '\n') {

src/tests/Makefile.am

@@ -53,7 +53,8 @@ test_at_serial_port_SOURCES = \
 
 test_at_serial_port_CPPFLAGS = \
 	$(MM_CFLAGS) \
-	-I$(top_srcdir)
+	-I$(top_srcdir) \
+	-I$(top_srcdir)/src
 
 test_at_serial_port_LDADD = \
 	$(MM_LIBS) \