NFSv4.1: Convert pNFS deviceid to use kfree_rcu()

Use of synchronize_rcu() when unmounting and potentially freeing a lot
of deviceids is problematic. There really is no reason why we can't just
use kfree_rcu() here.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/fs/nfs/filelayout/filelayoutdev.c b/fs/nfs/filelayout/filelayoutdev.c
index 4f372e2..4946ef4 100644
--- a/fs/nfs/filelayout/filelayoutdev.c
+++ b/fs/nfs/filelayout/filelayoutdev.c
@@ -55,7 +55,7 @@
 			nfs4_pnfs_ds_put(ds);
 	}
 	kfree(dsaddr->stripe_indices);
-	kfree(dsaddr);
+	kfree_rcu(dsaddr, id_node.rcu);
 }
 
 /* Decode opaque device data and return the result */