Clean up variables when closing BT

Clean up variables when closing BT to prevent using wrong objects.

Bug: 111716107
Test: manually adjust volume after unpair/pair
Change-Id: I3fd7de74aecbdacede3e73a5200568c265c0e202
(cherry picked from commit 2a592673f48b8e78a92f982884df64be845a8548)
1 file changed