[media] cec: add cec_phys_addr_invalidate() helper function

Simplifies setting the physical address to CEC_PHYS_ADDR_INVALID.

Change-Id: If7379ecdad3a02aea5499df459baf03c75623fe0
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Git-commit: 135327899d2874f2b65b3a3626b37d87df9e6a05
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Venkata Prahlad Valluru <vvalluru@codeaurora.org>