erofs: correct indentation of an assigned structure inside a function

Trivial change, the expected indentation ruled by the coding style
hasn't been met.

Signed-off-by: Vladimir Zapolskiy <vladimir@tuxera.com>
Link: https://lore.kernel.org/r/20200102120232.15074-1-vladimir@tuxera.com


Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>