media: videobuf2: use explicit unsigned int in vb2_queue

Switch from 'unsigned' to 'unsigned int' so that checkpatch doesn't
complain.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>