cmd/compile: fix irgen reports wrong error message for misuse of //go:embed

Fixes #48230

Change-Id: Ic6490e065e7e79793faa0d0201dc94f5fcea694a
Reviewed-on: https://go-review.googlesource.com/c/go/+/355529


Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Dan Scales <danscales@google.com>