pinctrl: mtk-common: Use devm_pinctrl_register() for pinctrl registration

Use devm_pinctrl_register() for pin control registration and clean
the error path.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Hongzhou Yang <hongzhou.yang@mediatek.com>
Cc: Yingjoe Chen <yingjoe.chen@mediatek.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Acked-by: Hongzhou Yang <hongzhou.yang@mediatek.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>