drm/amd: Fix the return for average power on aldebaran

Aldebaran can only return average socket power for the first die.
The other dies return 0.  Instead of returning a bad value, return
-EOPNOTSUPP so that the attribute will be hidden.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>