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

drivers/staging/vc04_services/bcm2835-audio/Kconfig

@@ -5,5 +5,7 @@ config SND_BCM2835
 	select SND_PCM
 	select BCM2835_VCHIQ
 	help
-	  Say Y or M if you want to support BCM2835 built in audio
-
+	  Say Y or M if you want to support BCM2835 built in audio.
+	  This driver handles both 3.5mm and HDMI audio, by leveraging
+	  the VCHIQ messaging interface between the kernel and the firmware
+	  running on VideoCore.
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