thermal: tools: tmon: remove unneeded local variable

Fix the following coccicheck review:
/tools/thermal/tmon/pid.c:57:5-8: Unneeded variable

Remove unneeded variable used to store return value.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: ran jianping <ran.jianping@zte.com.cn>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

tools/thermal/tmon/pid.c

@@ -54,7 +54,6 @@ static double xk_1, xk_2; /* input temperature x[k-#] */
  */
 int init_thermal_controller(void)
 {
-	int ret = 0;
 
 	/* init pid params */
 	p_param.ts = ticktime;
@@ -65,7 +64,7 @@ int init_thermal_controller(void)
 
 	p_param.t_target = target_temp_user;
 
-	return ret;
+	return 0;
 }
 
 void controller_reset(void)