btrfs: rename root fields in delayed refs structs

Both data and metadata delayed ref structures have fields named
root/ref_root respectively. Those are somewhat cryptic and don't really
convey the real meaning. In fact those roots are really the original
owners of the respective block (i.e in case of a snapshot a data delayed
ref will contain the original root that owns the given block). Rename
those fields accordingly and adjust comments.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/ref-verify.c b/fs/btrfs/ref-verify.c
index d2062d5..e2b9f86 100644
--- a/fs/btrfs/ref-verify.c
+++ b/fs/btrfs/ref-verify.c
@@ -678,10 +678,10 @@ int btrfs_ref_tree_mod(struct btrfs_fs_info *fs_info,
 
 	if (generic_ref->type == BTRFS_REF_METADATA) {
 		if (!parent)
-			ref_root = generic_ref->tree_ref.root;
+			ref_root = generic_ref->tree_ref.owning_root;
 		owner = generic_ref->tree_ref.level;
 	} else if (!parent) {
-		ref_root = generic_ref->data_ref.ref_root;
+		ref_root = generic_ref->data_ref.owning_root;
 		owner = generic_ref->data_ref.ino;
 		offset = generic_ref->data_ref.offset;
 	}