cmd/compile: move Heapaddr field from Name to Param

No performance impact, just cleanup.

Passes toolstash -cmp.

Change-Id: Ic7957d2686de53a9680c2bdefe926cccccd73a5c
Reviewed-on: https://go-review.googlesource.com/36316


Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>