Fix visibility of VariableDateView

Missing setVisibility in animation atStart. That way we make sure that
it's always in a visible state before we start expanding. When in
keyguard, the expansion is 1 (GONE), but then it'd jump to 0 (missing
set to VISIBLE).

Test: manual
Fixes: 198797641
Change-Id: Ia7d22f37085779b9412ea35333bcdf4a664ef693