Fix lint found by golangci-lint

Kubernetes-commit: 9cf189f4e029ee31ee0cdbf0e6365554a59b8ef4

Author: thockin

cmd/defaulter-gen/generators/defaulter.go

@@ -1201,13 +1201,13 @@ func (path callPath) String() string {
 			}
 		case p.index:
 			if len(parts) > 0 {
-				parts[last] = parts[last] + "[i]"
+				parts[last] += "[i]"
 			} else {
 				parts = append(parts, "[i]")
 			}
 		case p.key:
 			if len(parts) > 0 {
-				parts[last] = parts[last] + "[key]"
+				parts[last] += "[key]"
 			} else {
 				parts = append(parts, "[key]")
 			}

cmd/import-boss/main.go

@@ -429,7 +429,7 @@ func hasPathPrefix(path, prefix string) bool {
 		return true
 	}
 	if !strings.HasSuffix(path, string(filepath.Separator)) {
-		prefix = prefix + string(filepath.Separator)
+		prefix += string(filepath.Separator)
 	}
 	return strings.HasPrefix(path, prefix)
 }