all: fix issues reported by honnef.co/go/simple/cmd/gosimple

cmd/ethtest/main.go

@@ -88,12 +88,7 @@ func runTestWithReader(test string, r io.Reader) error {
 	default:
 		err = fmt.Errorf("Invalid test type specified: %v", test)
 	}
-
-	if err != nil {
-		return err
-	}
-
-	return nil
+	return err
 }
 
 func getFiles(path string) ([]string, error) {