NFS: Fix NFS4 callback up/down prototypes

Make the nfs_callback_up()/down() prototypes just do nothing if NFS4 is not
enabled.  Also make the down function void type since we can't really do
anything if it fails.

Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index d6c4bae..b1f7dc4 100644
--- a/fs/nfs/callback.c
+++ b/fs/nfs/callback.c
@@ -149,10 +149,8 @@
 /*
  * Kill the server process if it is not already up.
  */
-int nfs_callback_down(void)
+void nfs_callback_down(void)
 {
-	int ret = 0;
-
 	lock_kernel();
 	mutex_lock(&nfs_callback_mutex);
 	nfs_callback_info.users--;
@@ -164,7 +162,6 @@
 	} while (wait_for_completion_timeout(&nfs_callback_info.stopped, 5*HZ) == 0);
 	mutex_unlock(&nfs_callback_mutex);
 	unlock_kernel();
-	return ret;
 }
 
 static int nfs_callback_authenticate(struct svc_rqst *rqstp)