drm/amdgpu/smu8: return an error rather than 50% if busy query fails

For consistency with SMU10.
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/pm/powerplay/hwmgr/smu8_hwmgr.c

@@ -1788,11 +1788,10 @@ static int smu8_read_sensor(struct pp_hwmgr *hwmgr, int idx,
 		result = smum_send_msg_to_smc(hwmgr,
 				PPSMC_MSG_GetAverageGraphicsActivity,
 				&activity_percent);
-		if (0 == result) {
+		if (0 == result)
 			activity_percent = activity_percent > 100 ? 100 : activity_percent;
-		} else {
-			activity_percent = 50;
-		}
+		else
+			return -EIO;
 		*((uint32_t *)value) = activity_percent;
 		return 0;
 	case AMDGPU_PP_SENSOR_UVD_POWER: