That's dead in the water. You can never get that to work. I assume that function performs some logic on the input parameter. But all you have is a group of completely meaningless bytes, because the value is encrypted, and there is no way you can decrypt it inside SQL Server.
And if we overlook that small (well not so small) detail, the trigger is still wrong. As I said, you can't read something from inserted/deleted into a variable. (Unless you are running a cursor over the table, but please don't do that.
The above should be:
UPDATE myTable
CC_Key = dbo,myFunction(i.Type, i.CC_NO, i.FROM_DATE_TIME)
FROM myTable T
JOIN inserted i ON T.ID = i.ID
Note the FROM-JOIN clause.
But the above will not work as long as the column is encrypted. If you need the column encrypted, you need to re-think your approach.