btrfs: remove checks for a root with id 0 during backref walking

When doing backref walking to determine if an extent is shared, we are
testing the root_objectid of the given share_check struct is 0, but that
is an impossible case, since btrfs_is_data_extent_shared() always
initializes the root_objectid field with the id of the given root, and
no root can have an objectid of 0. So remove those checks.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/backref.c

@@ -719,8 +719,7 @@ static int resolve_indirect_refs(struct btrfs_fs_info *fs_info,
 			continue;
 		}
 
-		if (sc && sc->root_objectid &&
-		    ref->root_id != sc->root_objectid) {
+		if (sc && ref->root_id != sc->root_objectid) {
 			free_pref(ref);
 			ret = BACKREF_FOUND_SHARED;
 			goto out;
@@ -1348,8 +1347,7 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans,
 		 * and would retain their original ref->count < 0.
 		 */
 		if (roots && ref->count && ref->root_id && ref->parent == 0) {
-			if (sc && sc->root_objectid &&
-			    ref->root_id != sc->root_objectid) {
+			if (sc && ref->root_id != sc->root_objectid) {
 				ret = BACKREF_FOUND_SHARED;
 				goto out;
 			}