mmc: jz4740: Use PTR_ERR_OR_ZERO in jz4740_mmc_request_gpios()

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

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Joey Pabalinas <joeypabalinas@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>