drm/amd/powerplay: map mclk to fclk for COMBINATIONAL_BYPASS case

When hit COMBINATIONAL_BYPASS the mclk will be bypass and can export
fclk frequency to user usage.

Signed-off-by: Prike Liang <Prike.Liang@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org