archive: New() can't fail, so don't return an error type

It could fail if the system can't allocate memory or something
undeterministic like that, but in that case it's best to just let the
runtime panic.

cmd/mkinitfs/main.go

@@ -152,10 +152,7 @@ func generateArchive(name string, format archive.CompressFormat, level archive.C
 	log.Printf("- Using compression format %s with level %q\n", format, level)
 
 	defer misc.TimeFunc(time.Now(), name)
-	a, err := archive.New(format, level)
-	if err != nil {
-		return err
-	}
+	a := archive.New(format, level)
 
 	fs := initramfs.New(features)
 	if err := a.AddItems(fs); err != nil {