can: fix SJA1000 dlc for RTR packets

RTR frames do have a valid data length code on CAN.
The driver for SJA1000 did not handle that situation properly.
Signed-off-by: Kurt Van Dijck <kurt.van.dijck@eia.be>
Acked-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/can/sja1000/sja1000.c

@@ -346,10 +346,10 @@ static void sja1000_rx(struct net_device *dev)
 		    | (priv->read_reg(priv, REG_ID2) >> 5);
 	}
 
+	cf->can_dlc = get_can_dlc(fi & 0x0F);
 	if (fi & FI_RTR) {
 		id |= CAN_RTR_FLAG;
 	} else {
-		cf->can_dlc = get_can_dlc(fi & 0x0F);
 		for (i = 0; i < cf->can_dlc; i++)
 			cf->data[i] = priv->read_reg(priv, dreg++);
 	}