sh_eth: read MAC address registers only once

The code reading the MAHR/MALR registers in read_mac_address() is terribly
ineffective -- it reads MAHR 4 times and MALR 2 times, while it's enough to
read each register only once.  Use the local variables to achieve that,
somewhat beautifying the code while at it...
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/renesas/sh_eth.c

@@ -989,12 +989,15 @@ static void read_mac_address(struct net_device *ndev, unsigned char *mac)
 	if (mac[0] || mac[1] || mac[2] || mac[3] || mac[4] || mac[5]) {
 		memcpy(ndev->dev_addr, mac, ETH_ALEN);
 	} else {
-		ndev->dev_addr[0] = (sh_eth_read(ndev, MAHR) >> 24);
-		ndev->dev_addr[1] = (sh_eth_read(ndev, MAHR) >> 16) & 0xFF;
-		ndev->dev_addr[2] = (sh_eth_read(ndev, MAHR) >> 8) & 0xFF;
-		ndev->dev_addr[3] = (sh_eth_read(ndev, MAHR) & 0xFF);
-		ndev->dev_addr[4] = (sh_eth_read(ndev, MALR) >> 8) & 0xFF;
-		ndev->dev_addr[5] = (sh_eth_read(ndev, MALR) & 0xFF);
+		u32 mahr = sh_eth_read(ndev, MAHR);
+		u32 malr = sh_eth_read(ndev, MALR);
+
+		ndev->dev_addr[0] = (mahr >> 24) & 0xFF;
+		ndev->dev_addr[1] = (mahr >> 16) & 0xFF;
+		ndev->dev_addr[2] = (mahr >>  8) & 0xFF;
+		ndev->dev_addr[3] = (mahr >>  0) & 0xFF;
+		ndev->dev_addr[4] = (malr >>  8) & 0xFF;
+		ndev->dev_addr[5] = (malr >>  0) & 0xFF;
 	}
 }