gpio: zynq: initialize clock even without CONFIG_PM

When the PM initialization was moved in the commit referenced below, the
code enabling the clock was removed from the probe function. On
CONFIG_PM=y kernels, this is not a problem as the pm resume hook enables
the clock, but when power management is disabled, all those pm_*
functions are noops and the clock is never enabled resulting in a
dysfunctional gpio controller.

Put the clock initialization back to support CONFIG_PM=n.

Cc: stable@vger.kernel.org
Signed-off-by: Helmut Grohne <h.grohne@intenta.de>
Fixes: 3773c195

 ("gpio: zynq: Do PM initialization earlier to support gpio hogs")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>