audio: acquire lock in adev_set_voice_volume()

Acquire the audio device mutex before calling into ril
library in adev_set_voice_volume() to avoid concurrency with
other calls to ril from select_mode() or set_incall_device().

Bug 6626532.

Change-Id: I2347477b39ce46137a654047266b70dd691c021c
1 file changed