cli/command: PromptUserForCredentials: inline isDefaultRegistry

remove isDefaultRegistry and inline it where it's used; the code-comment
already outlines what we're looking for, so the intermediate var didn't
add much currently.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah

cli/command/registry.go

@@ -123,11 +123,10 @@ func PromptUserForCredentials(ctx context.Context, cli Cli, argUser, argPassword
 		cli.SetIn(streams.NewIn(os.Stdin))
 	}
 
-	isDefaultRegistry := serverAddress == registry.IndexServer
 	defaultUsername = strings.TrimSpace(defaultUsername)
 
 	if argUser = strings.TrimSpace(argUser); argUser == "" {
-		if isDefaultRegistry {
+		if serverAddress == registry.IndexServer {
 			// if this is a default registry (docker hub), then display the following message.
 			fmt.Fprintln(cli.Out(), "Log in with your Docker ID or email address to push and pull images from Docker Hub. If you don't have a Docker ID, head over to https://hub.docker.com/ to create one.")
 			if hints.Enabled() {