pinctrl: zynqmp: Drop pinctrl_unregister for devm_ registered device

It's not necessary to unregister pin controller device registered
with devm_pinctrl_register() and using pinctrl_unregister() leads
to a double free.

Fixes: fa99e701

 ("pinctrl: zynqmp: some code cleanups")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/20210729071905.3235953-1-yangyingliang@huawei.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>