Fix mismatched parameter of font scale change

Since commit d7032535, the 3rd parameter of ContentObserver#onChange
(@hide) is changed from userId to flags.

Bug: 150939131
Fix: 150932077
Test: ConfigChangeTests#testChangeFontScaleRelaunch
Change-Id: If1eb8dd3c7bf574d4d5a23a739208975ec3c0e44