cmd/compile: tighten exportWriter.qualifiedIdent signature
cmd/compile: tighten exportWriter.qualifiedIdent signature

It always takes an *ir.Name and would panic given anything else
anyway, so tighten the signature to match.

Change-Id: I44fec5c5cc6d7f0b9c59eb91c9f9633137485360
Reviewed-on: https://go-review.googlesource.com/c/go/+/314009
Trust: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>
Run-TryBot: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>
Reviewed-by: Cuong Manh Le <54b4457f1dff6823379654eb5867596497ba782f@gmail.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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