hashmap_add takes "struct hashmap_entry *"

This is less error-prone than "void *" as the compiler now
detects invalid types being passed.

Signed-off-by: Eric Wong <e@80x24.org>
Reviewed-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ref-filter.c

@@ -1568,7 +1568,7 @@ static void populate_worktree_map(struct hashmap *map, struct worktree **worktre
 			hashmap_entry_init(&entry->ent,
 					strhash(worktrees[i]->head_ref));
 
-			hashmap_add(map, entry);
+			hashmap_add(map, &entry->ent);
 		}
 	}
 }