cmd/compile: fix format error
cmd/compile: fix format error

Found by pending CL to make cmd/vet auto-detect printf wrappers.

Change-Id: I6b5ba8f9c301dd2d7086c152cf2e54a68b012208
Reviewed-on: https://go-review.googlesource.com/109345
Run-TryBot: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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