ARM: imx51: fix a leaked reference by adding missing of_node_put

The call to of_get_next_child returns a node pointer with refcount
incremented thus it must be explicitly decremented after the last
usage.

Detected by coccinelle with the following warnings:
./arch/arm/mach-imx/mach-imx51.c:64:2-8: ERROR: missing of_node_put; acquired a node pointer with refcount incremented on line 57, but without a corresponding object release within this function.
Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: NXP Linux Team <linux-imx@nxp.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/mach-imx/mach-imx51.c

@@ -59,6 +59,7 @@ static void __init imx51_m4if_setup(void)
 		return;
 
 	m4if_base = of_iomap(np, 0);
+	of_node_put(np);
 	if (!m4if_base) {
 		pr_err("Unable to map M4IF registers\n");
 		return;