media: ti-vpe: cal: Use ARRAY_SIZE to replace numerical value

Use ARRAY_SIZE(cal->ctx) to iterate over the cal->ctx array instead of
using the numerical value from the CAL_NUM_CONTEXT macro (or, worse,
hardcoding the value 2). This will allow reworking contexts with less
changes in the code.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>