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++)
                    ~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~