[sis190] Fix for gcc-3.3.3 compilation

gcc 3.3.3 gave the following error when compiling sis190.c

drivers/net/sis190.c: In function 'sis190_get_mac_addr_from_apc':
drivers/net/sis190.c:966: warning: 'isa_bridge' might be used
uninitialized in this function
make: *** [bin/sis190.o] Error 1

This patch allows error-free compilation.

Signed-off-by: Marty Connor <mdc@etherboot.org>

src/drivers/net/sis190.c

@@ -963,7 +963,7 @@ static int sis190_get_mac_addr_from_apc(struct pci_device *pdev,
 					struct net_device *dev)
 {
 	struct sis190_private *tp = netdev_priv(dev);
-	struct pci_device *isa_bridge;
+	struct pci_device *isa_bridge = NULL;
 	struct device *d;
 	u8 reg, tmp8;
 	unsigned int i;