bcachefs: Fix BTREE_FOREGROUND_MERGE_HYSTERESIS

We were multiplying instead of dividing - oops.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_cache.h

@@ -89,7 +89,7 @@ static inline unsigned btree_blocks(struct bch_fs *c)
 #define BTREE_FOREGROUND_MERGE_THRESHOLD(c)	(btree_max_u64s(c) * 1 / 3)
 #define BTREE_FOREGROUND_MERGE_HYSTERESIS(c)			\
 	(BTREE_FOREGROUND_MERGE_THRESHOLD(c) +			\
-	 (BTREE_FOREGROUND_MERGE_THRESHOLD(c) << 2))
+	 (BTREE_FOREGROUND_MERGE_THRESHOLD(c) >> 2))
 
 #define btree_node_root(_c, _b)	((_c)->btree_roots[(_b)->c.btree_id].b)