drm/amd/pm: correct the check for current link status

The output from metrics table for current link status changed.
We need to update our driver accordingly.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Likun Gao <Likun.Gao@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>