media: cec: integrate cec_validate_phys_addr() in cec-api.c

The cec_phys_addr_validate() function will be moved to V4L2,
so use a simplified variant of that function in cec-api.c.
cec now no longer calls cec_phys_addr_validate() and it can
be safely moved to V4L2.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: <stable@vger.kernel.org>      # for v4.17 and up
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>