SystemUI: Use proper lock icon scale on dismissing notification panel view

* I have no clue why 2.0f scale was used before,
  maybe it was some older AOSP leftover.
* Fixes too big lock icon after tapping mid
  swipe up animation on the lockscreen.

Test: When device is locked swipe up and tap on the screen
      during the animation; observe properly sized lock icon image.
Change-Id: Ifa4fda2871a8e1c7bb5300421602b1bc2c0cdbb9