media: staging: omap4iss: remove cacheflush import

The cacheflush import is never used, so it is safe to remove it as an
import.

Signed-off-by: Ian Cowan <ian@linux.cowan.aero>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>