lmc: Use memdup_user() as a cleanup

Fix coccicheck warning which recommends to use memdup_user():
drivers/net/wan/lmc/lmc_main.c:497:27-34: WARNING opportunity for memdup_user
Generated by: scripts/coccinelle/memdup_user/memdup_user.cocci
Signed-off-by: Vasyl Gomonovych <gomonovych@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/wan/lmc/lmc_main.c

@@ -494,16 +494,9 @@ int lmc_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd) /*fold00*/
                             break;
                     }
 
-                    data = kmalloc(xc.len, GFP_KERNEL);
-                    if (!data) {
-                            ret = -ENOMEM;
-                            break;
-                    }
-                    
-                    if(copy_from_user(data, xc.data, xc.len))
-                    {
-                    	kfree(data);
-                    	ret = -ENOMEM;
+                    data = memdup_user(xc.data, xc.len);
+                    if (IS_ERR(data)) {
+                            ret = PTR_ERR(data);
                             break;
                     }