media: vcodec: Fix potential array out-of-bounds in encoder queue_setup

variable *nplanes is provided by user via system call argument. The
possible value of q_data->fmt->num_planes is 1-3, while the value
of *nplanes can be 1-8. The array access by index i can cause array
out-of-bounds.

Fix this bug by checking *nplanes against the array size.

Fixes: 4e855a6e

 ("[media] vcodec: mediatek: Add Mediatek V4L2 Video Encoder Driver")
Signed-off-by: Wei Chen <harperchen1110@gmail.com>
Cc: stable@vger.kernel.org
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>