android: device: use size_t for loop index

Fix the following warning:

        ../../modules/audio_output/android/device.c:93:23: warning: comparison of integers of different signs: 'int' and 'unsigned long' [-Wsign-compare]
        for (int i = 0; i < ARRAY_SIZE(audio_output_by_soc); i++)
                        ~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

modules/audio_output/android/device.c

@@ -90,7 +90,7 @@ static enum AudioOutput get_audio_output_from_device(void)
 
     int len = 0;
     char value[PROP_VALUE_MAX];
-    for (int i = 0; i < ARRAY_SIZE(audio_output_by_soc); i++)
+    for (size_t i = 0; i < ARRAY_SIZE(audio_output_by_soc); i++)
     {
         /* On return, len will equal (int)strlen(model_id) */
         len = __system_property_get(audio_output_by_soc[i].property, value);