f2fs: fix wrong alloc_type in f2fs_do_replace_block

If the alloc_type of the original curseg is LFS,
when we change_curseg and then do recover curseg,
the alloc_type becomes SSR.

Signed-off-by: Wang Xiaojun <wangxiaojun11@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>