This driver is meant to be used with Device Tree and there's no
use-case where device's DT node is going to be NULL. Remove code
protecting against that.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: Chris Healy <cphealy@gmail.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Eduardo Valentin <edubezval@gmail.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: linux-imx@nxp.com
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org