can: xilinx_can: fix comparison of unsigned variable

The variable err was of the type u32. It was being compared with < 0, and being
an unsigned variable the comparison would have been always false.

Moreover, err was getting the return value from set_reset_mode() and
xcan_set_bittiming(), and both are returning int.
Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Reviewed-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/xilinx_can.c

@@ -300,7 +300,8 @@ static int xcan_set_bittiming(struct net_device *ndev)
 static int xcan_chip_start(struct net_device *ndev)
 {
 	struct xcan_priv *priv = netdev_priv(ndev);
-	u32 err, reg_msr, reg_sr_mask;
+	u32 reg_msr, reg_sr_mask;
+	int err;
 	unsigned long timeout;
 
 	/* Check if it is in reset mode */