Fix missing "1.0f - " in factored-out helper

Before submitting, `zoomOutAsScale` was extracted out from two places.
Unfortunately, I also broke the function in that extraction so that
it scaled up from 0.0f instead of down from 1.0f. Very bad.

Followup to 8af5e1a2

Test: atest AppZoomOutControllerTest
Test: atest NotificationShadeDepthControllerTest
Test: but also manual inspection this time
Bug: 391463550
Flag: com.android.systemui.spatial_model_pushback_in_shader
Change-Id: I600ff68bf0ed9e893878170748cde3596bc62679