svcrdma: Squelch compiler warning when SUNRPC_DEBUG is disabled

  CC [M]  net/sunrpc/xprtrdma/svc_rdma_transport.o
linux/net/sunrpc/xprtrdma/svc_rdma_transport.c: In function ‘svc_rdma_accept’:
linux/net/sunrpc/xprtrdma/svc_rdma_transport.c:452:19: warning: variable ‘sap’ set but not used [-Wunused-but-set-variable]
  struct sockaddr *sap;
                   ^

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>