Get the value of "SiteuseType" before user makes the update

Summary:

Get the value of "SiteuseType" before user makes the update

Content (required):

I have a "BeforeUpdate" trigger wherein I am trying to validate if the user is trying to update SiteuseType of address to "Bill_To" and if its "Bill_To" I should display an error and stop the user. Code snippet is as below

The issue I am facing is that I am able to get the SiteuseType value after the user has changed it, so its not entering "If" loop to display the error

I tried using getOriginalattributevalue, however it cannot be used in the context of SiteuseType