[media] cx88: return proper errors during fw load

Don't return -1, return a proper error.

Replace dprintk(0, ...) by pr_err since firmware load errors should just be
reported as an error.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>