omapfb: add missing of_node_put after of_device_is_available

Add an of_node_put when a tested device node is not available.

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

):

// <smpl>
@@
identifier f;
local idexpression e;
expression x;
@@

e = f(...);
... when != of_node_put(e)
    when != x = e
    when != e = x
    when any
if (<+...of_device_is_available(e)...+>) {
  ... when != of_node_put(e)
(
  return e;
|
+ of_node_put(e);
  return ...;
)
}
// </smpl>

Fixes: f76ee892 ("omapfb: copy omapdss & displays for omapfb")
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>