media: vivid: fix wrong pixel_array control size

The pixel_array control size was calculated incorrectly:
the dimensions were swapped (dims[0] should be the height), and the
values should be the width or height divided by PIXEL_ARRAY_DIV
and rounded up. So don't use roundup, but use DIV_ROUND_UP instead.

This bug is harmless in the sense that nothing will break, except that
it consumes way too much memory for this control.

Fixes: 6bc7643d ("media: vivid: add pixel_array test control")
Cc: <stable@vger.kernel.org>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>