lib/testutil/integration: fix error checking style

Change-Id: Id7e2825d91b9c04c09dbf5e01b7f7fc6cb469b79
diff --git a/lib/testutil/integration/util.go b/lib/testutil/integration/util.go
index 81e148a..f82b759 100644
--- a/lib/testutil/integration/util.go
+++ b/lib/testutil/integration/util.go
@@ -222,8 +222,7 @@
 }
 
 func writeStringOrDie(t *testing.T, f *os.File, s string) {
-	_, err := f.WriteString(s)
-	if err != nil {
+	if _, err := f.WriteString(s); err != nil {
 		t.Fatalf("Write() failed: %v", err)
 	}
 }