Fix failing BrightnessMappingStrategyTest

We recently ported the ambient light to screen brightness in nits
mapping to the display-device configi to make them display specific. During that, we broke the tests
for BrightnessMappingStrategyTest.

Bug: 248045938
Test: atest BrightnessMappingStrategyTest
Change-Id: I5941f84a95f07bd4b48070ba9361c2e437978971