media: Staging: media: omap4iss: Use WARN_ON() instead of BUG_ON()

Use WARN_ON() instead of BUG_ON() to avoid crashing the kernel.

Signed-off-by: Srishti Sharma <srishtishar@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>