net: niu: fix format string overflow warning:

We get a warning for the port_name string that might be longer than
six characters if we had more than 10 ports:

drivers/net/ethernet/sun/niu.c: In function 'niu_put_parent':
drivers/net/ethernet/sun/niu.c:9563:21: error: '%d' directive writing between 1 and 3 bytes into a region of size 2 [-Werror=format-overflow=]
  sprintf(port_name, "port%d", port);
                     ^~~~~~~~
drivers/net/ethernet/sun/niu.c:9563:21: note: directive argument in the range [0, 255]
drivers/net/ethernet/sun/niu.c:9563:2: note: 'sprintf' output between 6 and 8 bytes into a destination of size 6
  sprintf(port_name, "port%d", port);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/sun/niu.c: In function 'niu_pci_init_one':
drivers/net/ethernet/sun/niu.c:9538:22: error: '%d' directive writing between 1 and 3 bytes into a region of size 2 [-Werror=format-overflow=]
   sprintf(port_name, "port%d", port);
                      ^~~~~~~~
drivers/net/ethernet/sun/niu.c:9538:22: note: directive argument in the range [0, 255]
drivers/net/ethernet/sun/niu.c:9538:3: note: 'sprintf' output between 6 and 8 bytes into a destination of size 6

While we know that the port number is small, there is no harm in
making the format string two bytes longer to avoid the warning.
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/sun/niu.c

@@ -9532,7 +9532,7 @@ static struct niu_parent *niu_get_parent(struct niu *np,
 		p = niu_new_parent(np, id, ptype);
 
 	if (p) {
-		char port_name[6];
+		char port_name[8];
 		int err;
 
 		sprintf(port_name, "port%d", port);
@@ -9553,7 +9553,7 @@ static void niu_put_parent(struct niu *np)
 {
 	struct niu_parent *p = np->parent;
 	u8 port = np->port;
-	char port_name[6];
+	char port_name[8];
 
 	BUG_ON(!p || p->ports[port] != np);