fix a2dp: set sample rate to 48K

Change-Id: Iafbb507c855d06f201c34ba17bf6aee01177bcf4
snd_soc_msm: Fix "Speaker DMIC Stereo" device

- fixes e.g. mute WhatsApp audio messages

Change-Id: I5df6350603670e5abcd6f8d6264d1f8f1d83dafc
(cherry picked from commit 7a2c21cad1c3a85decf6aa0d541bd6afd199ed5f)