[dev.unified] cmd/compile/internal/walk: fix typo in debug print

[dev.unified] cmd/compile/internal/walk: fix typo in debug print

We want to print `init` here. We called `ir.TakeInit(r)` earlier, so
`r.Init()` always evaluates to nil at this point.

Change-Id: I196fdcfbf5e63c80b7bff0cce1881c9e58302501
Reviewed-on: https://go-review.googlesource.com/c/go/+/415239
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>