staging: erofs: use the wrapped PTR_ERR_OR_ZERO instead of open code

Just clean up and logic doesn't change.

Link: https://lists.01.org/pipermail/kbuild-all/2018-July/050766.html


Fixes: d72d1ce6 ("staging: erofs: add namei functions")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>