media: staging: media: zoran: fix counting buffer in reserve

After each capture, zoran driver complains that it remains some unused
buffer. This is due to a missing count handling.

Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>