cpufreq: imx6q: fix possible object reference leak

cpufreq: imx6q: fix possible object reference leak

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

Detected by coccinelle with the following warnings:
./drivers/cpufreq/imx6q-cpufreq.c:391:4-10: ERROR: missing of_node_put; acquired a node pointer with refcount incremented on line 348, but without a corresponding object release within this function.
./drivers/cpufreq/imx6q-cpufreq.c:395:3-9: ERROR: missing of_node_put; acquired a node pointer with refcount incremented on line 348, but without a corresponding object release within this function.

Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
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: linux-pm@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>