Btrfs: fix memory leak of chunks' extent map

As we're hold a ref on looking up the extent map, we need to drop the ref
before returning to callers.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

fs/btrfs/volumes.c

@@ -4488,6 +4488,7 @@ int btrfs_num_copies(struct btrfs_fs_info *fs_info, u64 logical, u64 len)
 		btrfs_crit(fs_info, "Invalid mapping for %Lu-%Lu, got "
 			    "%Lu-%Lu\n", logical, logical+len, em->start,
 			    em->start + em->len);
+		free_extent_map(em);
 		return 1;
 	}
 
@@ -4668,6 +4669,7 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info, int rw,
 		btrfs_crit(fs_info, "found a bad mapping, wanted %Lu, "
 			   "found %Lu-%Lu\n", logical, em->start,
 			   em->start + em->len);
+		free_extent_map(em);
 		return -EINVAL;
 	}