cmd/compile: use ONAME node directly from generated hash func

cmd/compile: use ONAME node directly from generated hash func

Same as CL 436436, but for hashfor.

However, this passes toolstash-check, because the order of compiling
functions do not change.

Change-Id: Icc7d042e9c28b0fe4bb40a2b98b7f60cf3549bd1
Reviewed-on: https://go-review.googlesource.com/c/go/+/436961
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>