m8: fix a2dp: set sample rate to 48K

Sets the sample rate for Bluetooth to 48k to fix issue where pausing
music while connected results in about 3 seconds of playback, then
silence, yet still shows as playing.

Change-Id: I3cdfcfb7073d24b32937ee25e7ec2f1243559ec5
(cherry picked from commit 8334e62e19dc1a49d10ffe98750832b49ac090b1)