[media] ttusb_dec: avoid the risk of go past buffer

Fixes this smatch warning:
	drivers/media/usb/ttusb-dec/ttusb_dec.c:243 ttusb_dec_handle_irq() error: buffer overflow 'rc_keys' 26 <= 126

As the RC keys should be enabled previously, via:
	set_bit(rc_keys[i], input_dev->keybit);

It wouldn't go past the buffer in practice. Yet, as bad
things may happen when going past buffer, it doesn't hurt adding
a check here.

While here, fix CodingStyle issues on the routine.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/usb/ttusb-dec/ttusb_dec.c

@@ -206,7 +206,7 @@ static void ttusb_dec_set_model(struct ttusb_dec *dec,
 
 static void ttusb_dec_handle_irq( struct urb *urb)
 {
-	struct ttusb_dec * dec = urb->context;
+	struct ttusb_dec *dec = urb->context;
 	char *buffer = dec->irq_buffer;
 	int retval;
 
@@ -227,25 +227,31 @@ static void ttusb_dec_handle_irq( struct urb *urb)
 			goto exit;
 	}
 
-	if( (buffer[0] == 0x1) && (buffer[2] == 0x15) )  {
-		/* IR - Event */
-		/* this is an fact a bit too simple implementation;
+	if ((buffer[0] == 0x1) && (buffer[2] == 0x15))  {
+		/*
+		 * IR - Event
+		 *
+		 * this is an fact a bit too simple implementation;
 		 * the box also reports a keyrepeat signal
 		 * (with buffer[3] == 0x40) in an intervall of ~100ms.
 		 * But to handle this correctly we had to imlemenent some
 		 * kind of timer which signals a 'key up' event if no
 		 * keyrepeat signal is received for lets say 200ms.
 		 * this should/could be added later ...
-		 * for now lets report each signal as a key down and up*/
+		 * for now lets report each signal as a key down and up
+		 */
+		if (buffer[4] - 1 < ARRAY_SIZE(rc_keys)) {
 			dprintk("%s:rc signal:%d\n", __func__, buffer[4]);
 			input_report_key(dec->rc_input_dev, rc_keys[buffer[4] - 1], 1);
 			input_sync(dec->rc_input_dev);
 			input_report_key(dec->rc_input_dev, rc_keys[buffer[4] - 1], 0);
 			input_sync(dec->rc_input_dev);
 		}
+	}
 
-exit:	retval = usb_submit_urb(urb, GFP_ATOMIC);
-	if(retval)
+exit:
+	retval = usb_submit_urb(urb, GFP_ATOMIC);
+	if (retval)
 		printk("%s - usb_commit_urb failed with result: %d\n",
 			__func__, retval);
 }