f2fs: fix to check return value of inc_valid_block_count()

In __replace_atomic_write_block(), we missed to check return value
of inc_valid_block_count(), for extreme testcase that f2fs image is
run out of space, it may cause inconsistent status in between SIT
table and total valid block count.

Cc: Daeho Jeong <daehojeong@google.com>
Fixes: 3db1de0e ("f2fs: change the current atomic write way")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -246,10 +246,16 @@ static int __replace_atomic_write_block(struct inode *inode, pgoff_t index,
 	} else {
 		blkcnt_t count = 1;
 
+		err = inc_valid_block_count(sbi, inode, &count);
+		if (err) {
+			f2fs_put_dnode(&dn);
+			return err;
+		}
+
 		*old_addr = dn.data_blkaddr;
 		f2fs_truncate_data_blocks_range(&dn, 1);
 		dec_valid_block_count(sbi, F2FS_I(inode)->cow_inode, count);
-		inc_valid_block_count(sbi, inode, &count);
+
 		f2fs_replace_block(sbi, &dn, dn.data_blkaddr, new_addr,
 					ni.version, true, false);
 	}