[media] media/pci/cobalt: fix Kconfig and build when SND is not enabled

Fix build errors in cobalt driver when CONFIG_SND is not enabled.
Fixes these build errors:

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_card_new" [drivers/media/pci/cobalt/cobalt.ko] undefined!
ERROR: "snd_card_free" [drivers/media/pci/cobalt/cobalt.ko] undefined!
ERROR: "snd_card_register" [drivers/media/pci/cobalt/cobalt.ko] undefined!
ERROR: "snd_pcm_new" [drivers/media/pci/cobalt/cobalt.ko] undefined!

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc:	Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>