drm/amd/pm: correct the reference clock for fan speed(rpm) calculation

Correct the reference clock as 25Mhz for SMU13 fan speed calculation.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org # 6.0.x, 6.1.x