drivers: thermal: add check when unregistering cpu cooling

This patch avoids NULL pointer accesses while unregistering
cpu cooling devices, in case a NULL pointer is received.

Cc: Zhang Rui <rui.zhang@intel.com>
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>

drivers/thermal/cpu_cooling.c

diff --git a/drivers/thermal/cpu_cooling.c b/drivers/thermal/cpu_cooling.c
index 5b3744e..d179028 100644
--- a/drivers/thermal/cpu_cooling.c
+++ b/drivers/thermal/cpu_cooling.c
@@ -498,8 +498,12 @@
  */
 void cpufreq_cooling_unregister(struct thermal_cooling_device *cdev)
 {
-	struct cpufreq_cooling_device *cpufreq_dev = cdev->devdata;
+	struct cpufreq_cooling_device *cpufreq_dev;
 
+	if (!cdev)
+		return;
+
+	cpufreq_dev = cdev->devdata;
 	mutex_lock(&cooling_cpufreq_lock);
 	cpufreq_dev_count--;