mtd: mpc5121_nfc: fix memory leak on error path

Add a call to of_node_put in the error handling code following a call to
of_find_compatible_node.

Signed-off-by: Julia Lawall <julia@diku.dk>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>