goprotobuf: change error() to errorf() since it takes a format argument. (silences govet)
goprotobuf: change error() to errorf() since it takes a format argument.
(silences govet)

R=dsymonds
CC=golang-dev
http://codereview.appspot.com/4413043

fuchsia-mirror/third_party-github.com-golang-protobuf,mwitkow-io/protobuf,daemonl/protobuf,ArtemTeleshev/go-protobuf,csuideal/protobuf,jeremyletang/protobuf,skyportsystems/go-protobuf,adnaan/protobuf,trdata/protobuf,skyportsystems/go-protobuf,alskjstl/protobuf,jmptrader/protobuf-1,tamird/protobuf-2,aoeu/protobuf,hailocab/protobuf,kung-foo/protobuf,fuchsia-mirror/third_party-github.com-golang-protobuf,francoishill/protobuf,ekle/protoc-gen-goweb_test,golang/protobuf,tamird/protobuf-2,velocity-toolkit/protobuf-1,qinlodestar/protobuf,ekle/protoc-gen-goweb,eduardiazf/protobuf,trdata/protobuf,jrbarron/protobuf,linkedin-inc/protobuf,golang/protobuf