Fix fixed source SetFrameRateTest expectation

The logic for determining fixed source multiples is changed to more
closely mimic the logic in the platform frame rate selection.
Before, the logic and threshold in the CTS were too strict so that it
had a stricter expectation than what the platform would select.

Test: atest SetFrameRateTest
Bug: 372367614
Flag: TEST_ONLY
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:a907854be9b552dc7b113871355558b7150b0ba7)
Merged-In: I4999753effd594e0630df4f23fdf9ebe25dbf793
Change-Id: I4999753effd594e0630df4f23fdf9ebe25dbf793