staging: bcm2835-audio: remove unused semaphores

This patch removes unused semaphores alsa_stream->buffers_update_sem
and alsa_stream->control_sem from struct bcm2835_alsa_stream

Signed-off-by: Aishwarya Pant <aishpant@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>