video: of: display_timing: delete unneeded test before of_node_put

Of_node_put supports NULL as its argument, so the initial test is not
necessary.  Furthermore, native_mode cannot be NULL at this point.

Suggested by Uwe Kleine-König.

The semantic patch that fixes this problem is as follows:
(http://coccinelle.lip6.fr/

)

// <smpl>
@@
expression e;
@@

-if (e)
   of_node_put(e);
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>