lvm: Use fmin, fmax for clamping output

Use fmin and fmax instead of if else blocks for clamping
Also minor cleanups where these are used.

Bug: 120944950
Test: lvm/tests/build_and_run_all_unit_tests.sh
Test: lvm/tests/build_and_run_all_unit_tests_reverb.sh

Change-Id: I36d293c6a79d869f9f0a8a4e26325fb8cc9c3c3a