[media] v4l: omap4iss: Signal fatal errors to the vb2 queue

When a fatal error occurs in the pipeline signal it to the vb2 queue
with a call to vb2_queue_error(). The queue will then take care to
return -EIO when preparing buffers, remove the driver-specific code that
now duplicates that check.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>