[media] v4l: omap4iss: Clean up file handle in open() and release()

Both functions initialize the file handle with v4l2_fh_init() and thus
need to call clean up with v4l2_fh_exit() as appropriate. Fix it.

Signed-off-by: Shailendra Verma <shailendra.v@samsung.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>