Fix taskbar bg delay for the case when user is going home.

The default value was not set. I decided to flip the variable to make
it more readable.

Bug: 345768019
Test: swipe up fast to go home, note no taskbar bg
      swipe up slow to reveal taskhome, note taskbar bg shows immediately
Flag: com.android.launcher3.enable_scaling_reveal_home_animation
Change-Id: I7fb4bbdce45a14312e42abcf71f7f0643376ddc6