[DLM] fix compile warning

This patch fixes a compile warning in lowcomms-tcp.c indicating that
kmem_cache_t is deprecated.
Signed-Off-By: Patrick Caulfield <pcaulfie@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/dlm/lowcomms-tcp.c

@@ -143,7 +143,7 @@ static DECLARE_WAIT_QUEUE_HEAD(lowcomms_recv_waitq);
 /* An array of pointers to connections, indexed by NODEID */
 static struct connection **connections;
 static DECLARE_MUTEX(connections_lock);
-static kmem_cache_t *con_cache;
+static struct kmem_cache *con_cache;
 static int conn_array_size;
 
 /* List of sockets that have reads pending */