media: atomisp:use ARRAY_SIZE() instead of open coding

The array_length() macro just duplicates ARRAY_SIZE(), so we can
delete it.

Signed-off-by: Allen Pais <allen.lkml@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>