net: ipmr: drop ip_mr_init() mrt_cachep null check as we'll panic if it fails

It's not necessary to check for null as SLAB_PANIC is used and we'll
panic if the alloc fails, so just drop it.
Signed-off-by: NNikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/ipmr.c

@@ -2677,8 +2677,6 @@ int __init ip_mr_init(void)
 				       sizeof(struct mfc_cache),
 				       0, SLAB_HWCACHE_ALIGN | SLAB_PANIC,
 				       NULL);
-	if (!mrt_cachep)
-		return -ENOMEM;
 
 	err = register_pernet_subsys(&ipmr_net_ops);
 	if (err)