thermal: Add comment explaining test for critical temperature

The code testing if a temperature should be emulated or not is
not obvious. Add a comment explaining why this test is done.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Reviewed-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>

drivers/thermal/thermal_core.c

@@ -498,6 +498,11 @@ int thermal_zone_get_temp(struct thermal_zone_device *tz, int *temp)
 			}
 		}
 
+		/*
+		 * Only allow emulating a temperature when the real temperature
+		 * is below the critical temperature so that the emulation code
+		 * cannot hide critical conditions.
+		 */
 		if (!ret && *temp < crit_temp)
 			*temp = tz->emul_temperature;
 	}