net: mpls: fix memdup.cocci warning

Simply use kmemdup instead of explicitly allocating and copying memory.

Generated by: scripts/coccinelle/api/memdup.cocci
Signed-off-by: GONG, Ruiqi <gongruiqi1@huawei.com>
Link: https://lore.kernel.org/r/20220406114629.182833-1-gongruiqi1@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/mpls/af_mpls.c

@@ -1527,10 +1527,9 @@ static int mpls_ifdown(struct net_device *dev, int event)
 					rt->rt_nh_size;
 				struct mpls_route *orig = rt;
 
-				rt = kmalloc(size, GFP_KERNEL);
+				rt = kmemdup(orig, size, GFP_KERNEL);
 				if (!rt)
 					return -ENOMEM;
-				memcpy(rt, orig, size);
 			}
 		}