drm/amdgpu/gmc6: Don't print MC client as it's unknown

drm/amdgpu/gmc6: Don't print MC client as it's unknown

The VM_CONTEXT1_PROTECTION_FAULT_MCCLIENT register
doesn't exist on GMC v6 so we can't print the MC client as a
string like we do on GMC v7-v8. However, we still print the
mc_id from VM_CONTEXT1_PROTECTION_FAULT_STATUS.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>