xilinx: Fix compiler warning

The time comparsion functions require arguments of type unsigned long
instead of (signed) long.

Signed-off-by: Manuel Schölling <manuel.schoelling@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_mdio.c b/drivers/net/ethernet/xilinx/xilinx_axienet_mdio.c
index d4abf47..3b67d60 100644
--- a/drivers/net/ethernet/xilinx/xilinx_axienet_mdio.c
+++ b/drivers/net/ethernet/xilinx/xilinx_axienet_mdio.c
@@ -19,7 +19,7 @@
 /* Wait till MDIO interface is ready to accept a new transaction.*/
 int axienet_mdio_wait_until_ready(struct axienet_local *lp)
 {
-	long end = jiffies + 2;
+	unsigned long end = jiffies + 2;
 	while (!(axienet_ior(lp, XAE_MDIO_MCR_OFFSET) &
 		 XAE_MDIO_MCR_READY_MASK)) {
 		if (time_before_eq(end, jiffies)) {