drm/amd/display: Handle Unknown Result for SMU Periodic Retraining on DCN2.1

[WHY & HOW]
Currently if VBIOSSMC_Result_UnknownCmd is returned as result of smu msg
there is no way to know.  Put 1 in param so if 1 is returned, this unknown case is handled.

Signed-off-by: Sung Lee <sung.lee@amd.com>
Acked-by: Bindu Ramamurthy <bindu.r@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>