Btrfs: fix em leak in find_first_block_group

We need to call free_extent_map() on the em we look up.

Signed-off-by: Josef Bacik <jbacik@fb.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index d5d3cfb..60d4ae7 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -9887,6 +9887,7 @@
 			} else {
 				ret = 0;
 			}
+			free_extent_map(em);
 			goto out;
 		}
 		path->slots[0]++;