[media] v4l: mem2mem_testdev: remove BKL usage

Remove usage of BKL by usign per-device mutex.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
CC: Pawel Osciak <pawel@osciak.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
1 file changed