[media] m5602_s5k83a: check return value of kthread_create

Function kthread_create() returns an ERR_PTR on error. However, in
function s5k83a_start(), its return value is used without validation.
This may result in a bad memory access bug. This patch fixes the bug.
Signed-off-by: Pan Bian <bianpan2016@163.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/usb/gspca/m5602/m5602_s5k83a.c

@@ -345,6 +345,11 @@ int s5k83a_start(struct sd *sd)
 	   to assume that there is no better way of accomplishing this */
 	sd->rotation_thread = kthread_create(rotation_thread_function,
 					     sd, "rotation thread");
+	if (IS_ERR(sd->rotation_thread)) {
+		err = PTR_ERR(sd->rotation_thread);
+		sd->rotation_thread = NULL;
+		return err;
+	}
 	wake_up_process(sd->rotation_thread);
 
 	/* Preinit the sensor */