[media] V4L2: (cosmetic) remove redundant use of unlikely()

BUG*() and WARN*() macros specify their conditions as unlikely, using
BUG_ON(unlikely(condition)) is redundant, remove it.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>