drm/amd/pm: Return -EOPNOTSUPP when can't read power limit

So that hwmon_attributes_visible() will see that the power2_cap
attributes should not be visible on GPUs that don't support
the get_power_limit() function.

This fixes an error when running the "sensors" command on SI.

Fixes: 12c958d ("drm/amd/pm: Expose ppt1 limit for gc_v9_5_0")
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: Timur Kristóf

drivers/gpu/drm/amd/pm/amdgpu_dpm.c

@@ -1569,7 +1569,7 @@ int amdgpu_dpm_get_power_limit(struct amdgpu_device *adev,
 	int ret = 0;
 
 	if (!pp_funcs->get_power_limit)
-		return -ENODATA;
+		return -EOPNOTSUPP;
 
 	mutex_lock(&adev->pm.mutex);
 	ret = pp_funcs->get_power_limit(adev->powerplay.pp_handle,