s2io: Fix warnings due to -Wunused-but-set-variable.

Most of these are cases where we are trying to read back a register
after a write to ensure completion.

Simply pre-fixing the readl() or readq() with "(void)" is sufficient
because these are volatile operations and the compiler cannot eliminate
them just because no real assignment takes place.

The case of free_rxd_blk()'s assignments to "struct buffAdd *ba" is a
real spurious assignment as this variable is completely otherwise
unused.

Signed-off-by: David S. Miller <[e-mail]>
Acked-by: Jon Mason <[e-mail]>

drivers/net/s2io.c

···
 static void fix_mac_address(struct s2io_nic *sp)
 {
 	struct XENA_dev_config __iomem *bar0 = sp->bar0;
-	u64 val64;
 	int i = 0;
 
 	while (fix_mac[i] != END_SIGN) {
 		writeq(fix_mac[i++], &bar0->gpio_control);
 		udelay(10);
-		val64 = readq(&bar0->gpio_control);
+		(void) readq(&bar0->gpio_control);
 	}
 }
 
···
 	int j;
 	struct sk_buff *skb;
 	struct RxD_t *rxdp;
-	struct buffAdd *ba;
 	struct RxD1 *rxdp1;
 	struct RxD3 *rxdp3;
 	struct mac_info *mac_control = &sp->mac_control;
···
 			memset(rxdp, 0, sizeof(struct RxD1));
 		} else if (sp->rxd_mode == RXD_MODE_3B) {
 			rxdp3 = (struct RxD3 *)rxdp;
-			ba = &mac_control->rings[ring_no].ba[blk][j];
 			pci_unmap_single(sp->pdev,
 					 (dma_addr_t)rxdp3->Buffer0_ptr,
 					 BUF0_LEN,

drivers/net/s2io.h

···
 #define LF	2
 static inline void SPECIAL_REG_WRITE(u64 val, void __iomem *addr, int order)
 {
-	u32 ret;
-
 	if (order == LF) {
 		writel((u32) (val), addr);
-		ret = readl(addr);
+		(void) readl(addr);
 		writel((u32) (val >> 32), (addr + 4));
-		ret = readl(addr + 4);
+		(void) readl(addr + 4);
 	} else {
 		writel((u32) (val >> 32), (addr + 4));
-		ret = readl(addr + 4);
+		(void) readl(addr + 4);
 		writel((u32) (val), addr);
-		ret = readl(addr);
+		(void) readl(addr);
 	}
 }