go/parser: use valid position when reporting an error (copy-paste bug)
go/parser: use valid position when reporting an error (copy-paste bug)

This is a follow-up on https://golang.org/cl/202581.

Updates #33649.

Change-Id: Ib078fed983792c5493bdbed6d33e21b86856894a
Reviewed-on: https://go-review.googlesource.com/c/go/+/204041
Run-TryBot: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>
Run-TryBot: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>
Reviewed-by: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>

nawawi/go,nawawi/go,golang/go,nawawi/go,akutz/go,CAFxX/go,CAFxX/go,CAFxX/go,nawawi/go,cloudflare/go,golang/go,cloudflare/go,CAFxX/go,golang/go,akutz/go,cloudflare/go,CAFxX/go,akutz/go,akutz/go,nawawi/go,akutz/go,nawawi/go,CAFxX/go,cloudflare/go,akutz/go,cloudflare/go,cloudflare/go,cloudflare/go,nawawi/go,golang/go,nawawi/go,cloudflare/go,akutz/go,CAFxX/go,CAFxX/go,golang/go,golang/go,golang/go,golang/go,akutz/go