[media] redrat3: change return argument on redrat3_send_cmd() to int

redrat3_send_cmd() can return an error or the read data. However,
it currently returns an u8, as reported by smatch:
	drivers/media/rc/redrat3.c:416 redrat3_send_cmd() warn: signedness bug returning '(-12)'
Signed-off-by: NMauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/rc/redrat3.c

@@ -405,7 +405,7 @@ static void redrat3_process_ir_data(struct redrat3_dev *rr3)
 }
 
 /* Util fn to send rr3 cmds */
-static u8 redrat3_send_cmd(int cmd, struct redrat3_dev *rr3)
+static int redrat3_send_cmd(int cmd, struct redrat3_dev *rr3)
 {
 	struct usb_device *udev;
 	u8 *data;