mmc: pxamci: Fix error return code in pxamci_probe

Fix to return the error code from devm_gpiod_get_optional() instaed
of 0 in pxamci_probe().

Fixes: f54005b5 ("mmc: pxa: Use GPIO descriptor for power")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Link: https://lore.kernel.org/r/20201121021431.3168506-1-chengzhihao1@huawei.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>