[media] s5p-fimc: Do not lock both buffer queues in s_fmt

It is not necessary to lock both capture and output buffer queue while
setting format for single queue.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>