video: display_timing: make parameter const

As the device_node pointer is not changed in of_get_display_timing and
parse_timing_property it can be a const pointer.

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Dave Airlie <airlied@redhat.com>
1 file changed