Btrfs: remove BUG() in add_data_reference

Now that we have a helper to report invalid value of extent inline ref
type, we need to quit gracefully instead of throwing out a kernel panic.
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/relocation.c

@@ -3772,7 +3772,10 @@ int add_data_references(struct reloc_control *rc,
 			ret = find_data_references(rc, extent_key,
 						   eb, dref, blocks);
 		} else {
-			BUG();
+			ret = -EINVAL;
+			btrfs_err(rc->extent_root->fs_info,
+		     "extent %llu slot %d has an invalid inline ref type",
+			     eb->start, path->slots[0]);
 		}
 		if (ret) {
 			err = ret;