cmd/compile: fix TestFormats by using valid formats
cmd/compile: fix TestFormats by using valid formats

CL 142517 has used some formats incorrectly. This change fixes it
by using %v for errors and invoking Block.Kind.String().
Format map stays intact.

Updates #28177

Change-Id: If53b6cc54ba3c1ffc17b005225787e3b546de404
Reviewed-on: https://go-review.googlesource.com/c/150798
Run-TryBot: Yury Smolsky <f26331c55f2e9b348f65eb11cafdbe38d0f7ac5e@smolsky.by>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: David Chase <ae171625adc8645b8b79b7e405a6da5aba5341e0@google.com>

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