net: trans_rdma: remove unused function

This patch gets rid of the following warning:

net/9p/trans_rdma.c:594:12: warning: ‘rdma_cancelled’ defined but not used [-Wunused-function]
 static int rdma_cancelled(struct p9_client *client, struct p9_req_t *req)

The rdma_cancelled function is not called anywhere in the kernel

Signed-off-by: Andi Shyti <andi@etezian.org>
Signed-off-by: David S. Miller <davem@davemloft.net>