sh-pfc: Use PTR_ERR_OR_ZERO() to simplify the code

Use PTR_ERR_OR_ZERO rather than if(IS_ERR(...)) + PTR_ERR.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>