cli/command: RegistryAuthenticationPrivilegedFunc: fix hints for login

The RegistryAuthenticationPrivilegedFunc has some conditional logic to
add additional hints when logging in to the default (Docker Hub) registry.
Commit 9f4165c inadvertently passed the
wrong variable to PromptUserForCredentials, which caused it to show the
additional hints for Docker Hub.

Before this patch, hints were printed for the default (docker hub) registry;

    docker pull icr.io/my-ns/my-image:latest

    Login prior to pull:
    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.
    You can log in with your password or a Personal Access Token (PAT). Using a limited-scope PAT grants better security and is required for organizations using SSO. Learn more at https://docs.docker.com/go/access-tokens/

    Username:

With this patch, those hints are omitted;

    docker pull icr.io/my-ns/my-image:latest

    Login prior to pull:
    Username:

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

Author: thaJeztah

cli/command/registry.go

@@ -43,7 +43,7 @@ func RegistryAuthenticationPrivilegedFunc(cli Cli, index *registrytypes.IndexInf
 		_, _ = fmt.Fprintf(cli.Out(), "\nLogin prior to %s:\n", cmdName)
 		authConfig, err := GetDefaultAuthConfig(cli.ConfigFile(), true, configKey, isDefaultRegistry)
 		if err != nil {
-			_, _ = fmt.Fprintf(cli.Err(), "Unable to retrieve stored credentials for %s, error: %s.\n", authConfigKey, err)
+			_, _ = fmt.Fprintf(cli.Err(), "Unable to retrieve stored credentials for %s, error: %s.\n", configKey, err)
 		}
 
 		select {
@@ -52,7 +52,7 @@ func RegistryAuthenticationPrivilegedFunc(cli Cli, index *registrytypes.IndexInf
 		default:
 		}
 
-		authConfig, err = PromptUserForCredentials(ctx, cli, "", "", authConfig.Username, authConfigKey)
+		authConfig, err = PromptUserForCredentials(ctx, cli, "", "", authConfig.Username, configKey)
 		if err != nil {
 			return "", err
 		}