NFS,SUNRPC: Fix compiler warnings if CONFIG_PROC_FS & CONFIG_SYSCTL are unset

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
index 7eebbab..e8bbe81 100644
--- a/include/linux/sunrpc/xprt.h
+++ b/include/linux/sunrpc/xprt.h
@@ -53,6 +53,7 @@
 
 struct rpc_task;
 struct rpc_xprt;
+struct seq_file;
 
 /*
  * This describes a complete RPC request