runtime: fix makemap64 function signature

During rebase of golang.org/cl/55152 the bucket argument
which was removed in golang.org/cl/56290 from makemap
was not removed from the argument list of makemap64.

This did lead to "pointer in unallocated span" errors
on 32bit platforms since the compiler did only generate
calls to makemap64 without the bucket argument.

Fixes #21568

Change-Id: Ia964a3c285837cd901297f4e16e40402148f8c1c
Reviewed-on: https://go-review.googlesource.com/57990Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/hashmap.go

@@ -255,7 +255,7 @@ func (h *hmap) createOverflow() {
 	}
 }
 
-func makemap64(t *maptype, hint int64, h *hmap, bucket unsafe.Pointer) *hmap {
+func makemap64(t *maptype, hint int64, h *hmap) *hmap {
 	if int64(int(hint)) != hint {
 		hint = 0
 	}