pinctrl/amd: 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: 3bfd44306c65 ("pinctrl: amd: Add support for additional GPIO")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>