media: ov7640: Use ARRAY_SIZE instead of manual checking

Currently, the driver ends the reg-val list with a 0xFF as a check to stop
the loop. Instead an array of reg-vals can be used to avoid this check,
by using the ARRAY_SIZE(arr) macro to obtain the length of the array and
iterate over it.

Signed-off-by: Moses Christopher Bollavarapu <mosescb.dev@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>