[media] V4L: fix a compiler warning

Fix the warning:

In file included from /home/lyakh/software/project/24/src/linux-2.6/drivers/media/video/v4l2-subdev.c:29:
linux-2.6/include/media/v4l2-ctrls.h:497: warning: 'struct file' declared inside parameter list
linux-2.6/include/media/v4l2-ctrls.h:497: warning: its scope is only this definition or declaration, which is probably not what you want
linux-2.6/include/media/v4l2-ctrls.h:505: warning: 'struct file' declared inside parameter list

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>