There is a feature starting from Service Catalog 14.1 Cum 1 that allows you to change the URL and point to USS instead of Service Catalog for the email notification link.
Here are the steps to configure the URL to point to USS:
1) Log into Catalog as Service Delivery Administrator
2) Catalog tab > Configuration > Options > Request Management Configuration
3) Locate for "Request Details Link for Email Notifications" option
4) By default, value for this parameter is not configured.
This parameter can be configured in the following format if CA Service Catalog is configured with USS:
If Unified Self-Service (USS) URL is configured for Request Details Link for E-Mail Notifications,
clicking on the request details hyperlinks in the email notification will take to the Unified Self-Service login page instead of CA Service Catalog login page.
If this parameter is not configured, clicking on the hyperlinks in email notification with request details takes to the CA Service Catalog Login page.