Initialize the small frame in KeyguardClockSwitch as invisible

The KeyguardClockSwitch starts with the small clock frame as visible,
which allows the clock to be seen in a bad state if it's bound before
switchToClock is called with the appropriate clock size.

Fixes: 247608708
Test: Manually checked large & small clock user switch
Change-Id: I0885d19e297ff5f881271ed0347e9699b3494928