go/internal/gcimporter: add missing argument to error message

Change-Id: I3071f0e876506c6dc283e97bc15f157bf2ff011e
Reviewed-on: https://go-review.googlesource.com/19641Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/internal/gcimporter/gcimporter.go

@@ -385,7 +385,7 @@ func (p *parser) getPkg(id, name string) *types.Package {
 		if pname := pkg.Name(); pname == "" {
 			pkg.SetName(name)
 		} else if pname != name {
-			p.errorf("%s package name mismatch: %s (given) vs %s (expected)", pname, name)
+			p.errorf("%s package name mismatch: %s (given) vs %s (expected)", id, pname, name)
 		}
 	}
 	return pkg