The cobalt sound driver has a dependency on ALSA, but not
on the PCM helper code, so this can lead to an extremely
rare link error in randconfig builds:

ERROR: "snd_pcm_period_elapsed" [drivers/media/pci/cobalt/cobalt.ko] undefined!
ERROR: "_snd_pcm_stream_lock_irqsave" [drivers/media/pci/cobalt/cobalt.ko] undefined!
ERROR: "snd_pcm_hw_constraint_integer" [drivers/media/pci/cobalt/cobalt.ko] undefined!
ERROR: "snd_pcm_set_ops" [drivers/media/pci/cobalt/cobalt.ko] undefined!
ERROR: "snd_pcm_stream_unlock_irqrestore" [drivers/media/pci/cobalt/cobalt.ko] undefined!
ERROR: "snd_pcm_lib_ioctl" [drivers/media/pci/cobalt/cobalt.ko] undefined!
ERROR: "snd_pcm_new" [drivers/media/pci/cobalt/cobalt.ko] undefined!

The other audio drivers select 'SND_PCM' for this, so let's
do the same.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>