Fix the call the onFrameDequeued inside dequeueBuffer

Having a separate mutex lock for calling onFrameDequeued at the end of
the dequeueBuffer function seems to be problematic since there is a
chance that the buffer can be acquired before obtaining this lock
resulting in a null pointer dereference. Moving the call inside the
existing auto-lock scoped blocks in this CL.

Test: CtsCameraTestCases:MultiViewTest#testSharedSurfaceYUVImageReaderSwitch on blueline and crosshatch
Bug: 143542027
Change-Id: If9e4b36ca2c54337eb0e5a6647773db20e43a6a3