staging: bcm2835-audio: fully describe config symbol

Explain SND_BCM2835 config option in more detail to fix checkpatch
warning:

WARNING: please write a help paragraph that fully describes the config
symbol
FILE: drivers/staging/vc04_services/bcm2835-audio/Kconfig:2

Signed-off-by: Adrien Thierry <athierry@redhat.com>
Link: https://lore.kernel.org/r/20220414181622.102049-2-athierry@redhat.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>