thermal: qoriq: Remove unnecessary DT node is NULL check

It's impossible to use this driver outside of Device Tree, so if the
probe function is called, the dev.of_node is guaranteed to not be NULL
and guarding against that is pointless. Drop it.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Chris Healy <cphealy@gmail.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Eduardo Valentin <edubezval@gmail.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Angus Ainslie (Purism) <angus@akkea.ca>
Cc: linux-imx@nxp.com
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>