[media] exynos4-is: Add missing 'of_node_put'

It is likely that a "of_node_put(ep)" is missing here.
There is one in the previous error handling code, and one a few lines
below in the normal case as well.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>