[media] v4l2-fh: Include linux/fs.h for struct file definition

v4l2-fh.h dereferences struct file, the structure must thus be defined.
Pull in its definition by including linux/fs.h.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>