Merge "btaa: null check btaa instance when receiving callback from...

Merge "btaa: null check btaa instance when receiving callback from SystemSuspend" am: e7346e17 am: fff9547d

Original change: https://android-review.googlesource.com/c/platform/system/bt/+/1501012

Change-Id: I0eaadd9d9c434c37f51babddf46503df1ed66244