media: Use wait_queue_head_t for media_request

The portable type for a wait queue is wait_queue_head_t.

Signed-off-by: Jasmin Jessich <jasmin@anw.at>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>