[media] ddbridge: fix wait_event_timeout return handling

API conformance testing for completions with coccinelle spatches are being
used to locate API usage inconsistencies:
./drivers/media/pci/ddbridge/ddbridge-core.c:89
        incorrect check for negative return

Return type of wait_event_timeout is signed long not int and the
return type is >=0 always thus the negative check is unnecessary..
As stat is used here exclusively its type is simply changed and the
negative return check dropped.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>