keep a wp<BLASTBufferQueue> in BufferItemConsumer

Use a wp<> instead of raw pointer and remove the mutex around it
to prevent potential deadlocks.

Bug: 208121127
Test: stress test by partner
Test: atest BLASTBufferQueueTest
Change-Id: Iffed80410aeffc9b724d5c01ca2ec589c9622990
2 files changed