[media] MAINTAINERS: change entry for davinci media driver

As of now TI has no maintainer/supporter for davinci media
drivers, Until it has any I'll be maintaining it.

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>