Fix screen freeze when changing display size in Multi-Window mode

The device screen freezes when launching two Display size settings
screen and changing display size in Multi-Window mode.
To fix this issue, OnSeekBarChangeListener should be set in onStart() to
avoid onProgressChanged() is called during onRestoreInstanceState which
is caused by display size change.

Fixes: 70253030
Test: manual - open two Display size settings in Multi-Window mode.

Change-Id: I779954aeeb1da526ba1b0fac2676e2f7d8289352