staging: bcm2835-audio: Remove unnecessary header file includes

Yet a few header files are included unnecessarily.  Drop them.

Also remove trivial comments.

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>