SystemUI: fix hidden clock style after a reboot

Selecting hidden clock style and rebooting the device results
in both center and default clocks appearing when you'd expect
to see none.

mClockView is null after a reboot so visibility gets never set.
Set default visibility for clocks to gone.

Change-Id: I533af8c28042a5989e0025df133c9ccf1fa3e066
Merge "SystemUI: fix hidden clock style after a reboot" into pac-4.4