staging: bcm2835-audio: Remove redundant function calls

bcm2835_audio_setup(), bcm2835_audio_flush_buffers() and
bcm2835_audio_flush_playback_buffers() functions do implement
nothing.

Also, bcm2835_audio_set_ctls() is already called inside
bcm2835_audio_set_params(), so the later call is superfluous.

This patch removes these superfluous implementations.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>