cmd/compile: assign results of transformAssign back to source location
Otherwise the modifications of transformAssign are dropped on the floor.
Change-Id: Id40782564952ed53f9ade1dba4e85290c8522abc
Reviewed-on: https://go-review.googlesource.com/c/go/+/346590
Trust: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Dan Scales <danscales@google.com>