Fixed wrong value passed to -[UITableView setSeparatorStyle:]

A **cell selection style** was erroneously passed to `UITableView`'s **separatorStyle**.

This also caused a warning:
```
UAInboxMessageListController.m:272:42: Implicit conversion from enumeration type 'enum UITableViewCellSelectionStyle' to different enumeration type 'UITableViewCellSeparatorStyle' (aka 'enum UITableViewCellSeparatorStyle')
```