drivers/net/usb: Use kmemdup

Use kmemdup when some other buffer is immediately copied into the
allocated region.

A simplified version of the semantic patch that makes this change is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@@
expression from,to,size,flag;
statement S;
@@

-  to = \(kmalloc\|kzalloc\)(size,flag);
+  to = kmemdup(from,size,flag);
   if (to==NULL || ...) S
-  memcpy(to, from, size);
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/dm9601.c

@@ -93,10 +93,9 @@ static int dm_write(struct usbnet *dev, u8 reg, u16 length, void *data)
 	netdev_dbg(dev->net, "dm_write() reg=0x%02x, length=%d\n", reg, length);
 
 	if (data) {
-		buf = kmalloc(length, GFP_KERNEL);
+		buf = kmemdup(data, length, GFP_KERNEL);
 		if (!buf)
 			goto out;
-		memcpy(buf, data, length);
 	}
 
 	err = usb_control_msg(dev->udev,