media: cx88: use ARRAY_SIZE

Use ARRAY_SIZE instead of dividing sizeof array with sizeof an element

Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>