net: sxgbe: make "core_ops" static

The "core_ops" variable isn't referenced outside this file and Sparse
complains about it:

	drivers/net/ethernet/samsung/sxgbe/sxgbe_core.c:239:29: warning:
	symbol 'core_ops' was not declared. Should it be static?
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/samsung/sxgbe/sxgbe_core.c

@@ -236,7 +236,7 @@ static void sxgbe_disable_rx_csum(void __iomem *ioaddr)
 	writel(ctrl, ioaddr + SXGBE_CORE_RX_CONFIG_REG);
 }
 
-const struct sxgbe_core_ops core_ops = {
+static const struct sxgbe_core_ops core_ops = {
 	.core_init		= sxgbe_core_init,
 	.dump_regs		= sxgbe_core_dump_regs,
 	.host_irq_status	= sxgbe_core_host_irq_status,