[media] MAINTAINERS: fix drivers/media/platform/atmel-isi.c

This file was moved to drivers/media/platform/soc_camera/atmel-isi.c by
commit b47ff4a3 ([media] move soc_camera to its own directory).

Cc: Josh Wu <josh.wu@atmel.com>
Signed-off-by: Cesar Eduardo Barros <cesarb@cesarb.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>