media: video-i2c: fix buffer queue ordering

media: video-i2c: fix buffer queue ordering

Queued buffers are added to the tail of vid_cap_active in
buffer_queue(), but the capture kthread also retrieves buffers from
the tail of the list.

This makes the queue behave as LIFO instead of FIFO when multiple
buffers are queued.

Fix this by retrieving buffers from the head of the list.

Signed-off-by: Arash Golgol <arash.golgol@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>