staging: bcm2835-audio: fix empty-body warning

gcc-7 warns about debug statements being left out here:

drivers/staging/bcm2835-audio/bcm2835-vchiq.c: In function 'bcm2835_audio_set_ctls':
drivers/staging/bcm2835-audio/bcm2835-vchiq.c:572:54: error: suggest braces around empty body in an 'else' statement [-Werror=empty-body]

It's better to use no_printk(), which has the added advantage of checking
the format strings.

Fixes: 23b028c8 ("staging: bcm2835-audio: initial staging submission")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>