Settings: fix ShowRefreshRatePreferenceControllerTest

ShowRefreshRatePreferenceControllerTest is using an incorrect type
(Int vs. Bool) which causing a test to fail.

Bug: 146767072
Test: make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.development
Change-Id: I9269c01619eebac9c0eac29e23f248d1c6d48ba5