drm/amd/display: Fix and simplify apply_below_the_range()

The comparison of inserted_frame_duration_in_us against a
duration calculated from max_refresh_in_uhz is both wrong
in its math and not needed, as the min_duration_in_us value
is already cached in in_out_vrr for reuse. No need to
recalculate it wrongly at each invocation.

Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>