Settings: fixed being able to activate only one keyboard per session

The bug is that in the "Language & Keyboard" screen, you can only
activate one keyboard until you press back and enter the screen
again.

mDialog must be recreated every round because the mDialog instance
contains chkPref and id which must be updated for every activation.

Change-Id: I7412a3d954857698e0cb02c0cafe036372f131bf