Fix 6028595: Fix reboot loop in AccountUnlock due to null callback

This fixes a bug where the device would get into a reboot loop due to having
a null callback.  The problem was that a recent change caused the callback
to be used indirectly by the constructor before being set.

The solution is to pass the callback to the KeyguardViewBase constructor
which ensures it's ready by the time we call getCallback().

Change-Id: I2598fc5338be99977980e4dea41a096fb2a7ef7e