pinctrl: Fix return value about devm_platform_ioremap_resource()

When call function devm_platform_ioremap_resource(), we should use IS_ERR()
to check the return value and return PTR_ERR() if failed.

Fixes: 4b024225 ("pinctrl: use devm_platform_ioremap_resource() to simplify code")
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Link: https://lore.kernel.org/r/1590234326-2194-1-git-send-email-yangtiezhu@loongson.cn


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>