svcrdma: Remove unused variables in xprt_rdma_bc_allocate()

Clean up.

/linux-2.6/net/sunrpc/xprtrdma/svc_rdma_backchannel.c: In function
 ‘xprt_rdma_bc_allocate’:
linux-2.6/net/sunrpc/xprtrdma/svc_rdma_backchannel.c:169:23: warning:
 variable ‘rdma’ set but not used [-Wunused-but-set-variable]
  struct svcxprt_rdma *rdma;
                       ^

Fixes: 5d252f90 ("svcrdma: Add class for RDMA backwards ...")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

net/sunrpc/xprtrdma/svc_rdma_backchannel.c

@@ -164,13 +164,9 @@ static int
 xprt_rdma_bc_allocate(struct rpc_task *task)
 {
 	struct rpc_rqst *rqst = task->tk_rqstp;
-	struct svc_xprt *sxprt = rqst->rq_xprt->bc_xprt;
 	size_t size = rqst->rq_callsize;
-	struct svcxprt_rdma *rdma;
 	struct page *page;
 
-	rdma = container_of(sxprt, struct svcxprt_rdma, sc_xprt);
-
 	if (size > PAGE_SIZE) {
 		WARN_ONCE(1, "svcrdma: large bc buffer request (size %zu)\n",
 			  size);