pinctrl: tb10x: fix the error handling in tb10x_pinctrl_probe()

This patch fix the error handling in tb10x_pinctrl_probe():
 - devm_ioremap_resource() return ERR_PTR() and never return NULL
 - remove the dev_err call to avoid redundant error message
 - pinctrl_register() returns NULL not ERR_PTR()

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>