iOS: Use right DPI for all iPad Minis, not just the WiFi version

The 3G versions are iPad2,6 and iPad2,7.

Change-Id: I43a00e84535d494550bca8a533a6d16af4be6722
Reviewed-by: Ian Dean <ian@mediator-software.com>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>