[media] rainshadow-cec: Fix missing spin_lock_init()

The driver allocates the spinlock but not initialize it.
Use spin_lock_init() on it to initialize it correctly.

This is detected by Coccinelle semantic patch.

Fixes: 0f314f6c ("[media] rainshadow-cec: new RainShadow Tech HDMI
CEC driver")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/usb/rainshadow-cec/rainshadow-cec.c

@@ -336,6 +336,7 @@ static int rain_connect(struct serio *serio, struct serio_driver *drv)
 	serio_set_drvdata(serio, rain);
 	INIT_WORK(&rain->work, rain_irq_work_handler);
 	mutex_init(&rain->write_lock);
+	spin_lock_init(&rain->buf_lock);
 
 	err = serio_open(serio, drv);
 	if (err)