f2fs: fix memory leak of write_io in fill_super()

[ Upstream commit 0b2103e886e6de9802e1170e57c573443286a483 ]

It needs to release memory allocated for sbi->write_io in error path,
otherwise, it will cause memory leak.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>