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 am: b4388dba am: 0f1c381d

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

Change-Id: I690395fa860ec2b76de0f2ad5ff274c281660ec7