bcachefs: Inline bch2_snapshot_is_ancestor() fast path

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/subvolume.c

@@ -25,7 +25,7 @@ static inline u32 get_ancestor_below(struct snapshot_table *t, u32 id, u32 ances
 	return s->parent;
 }
 
-bool bch2_snapshot_is_ancestor(struct bch_fs *c, u32 id, u32 ancestor)
+bool __bch2_snapshot_is_ancestor(struct bch_fs *c, u32 id, u32 ancestor)
 {
 	struct snapshot_table *t;
 	bool ret;

fs/bcachefs/subvolume.h

@@ -166,7 +166,14 @@ static inline u32 bch2_snapshot_sibling(struct bch_fs *c, u32 id)
 	return 0;
 }
 
-bool bch2_snapshot_is_ancestor(struct bch_fs *, u32, u32);
+bool __bch2_snapshot_is_ancestor(struct bch_fs *, u32, u32);
+
+static inline bool bch2_snapshot_is_ancestor(struct bch_fs *c, u32 id, u32 ancestor)
+{
+	return id == ancestor
+		? true
+		: __bch2_snapshot_is_ancestor(c, id, ancestor);
+}
 
 static inline bool bch2_snapshot_has_children(struct bch_fs *c, u32 id)
 {