Remove usage of "inverse" color.

This value has been removed from the support library. Instead, fix the
color to light as the user switcher is always dark.

Bug: 112040188
Test: built system UI and ensure that the color is always light for the
user switcher ripple

Change-Id: I49dae3b6869fa04aadf962ef8ddb0a6d2c2c8e37