cmd/compile: print pointers to go:notinheap types without converting to unsafe.Pointer

Pretty minor concern, but after auditing the compiler/runtime for
conversions from pointers to go:notinheap types to unsafe.Pointer,
this is the only remaining one I found.

Update #42076

Change-Id: I81d5b893c9ada2fc19a51c2559262f2e9ff71c35
Reviewed-on: https://go-review.googlesource.com/c/go/+/265757


Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>