staging: bcm2835-audio: Validate values written to controls

staging: bcm2835-audio: Validate values written to controls

The bcm2835-audio driver makes no effort to validate the values it accepts
from userspace, causing it to accept invalid values:

# # PCM Playback Switch.0 Invalid boolean value 2
# not ok 5 write_invalid.Headphones.1
# # PCM Playback Volume.0 value -10240 less than minimum -10239
# # PCM Playback Volume.0 value 401 more than maximum 400
# not ok 12 write_invalid.Headphones.0

Add validation.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20250415-staging-bcm2835-alsa-limit-v1-1-4ed816e9c0fc@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>