NFS: Fix atime revalidation in readdir()

NFSv3 will correctly update atime on a readdir call, so there is no need to
set the NFS_INO_INVALID_ATIME flag unless the call to nfs_refresh_inode()
fails.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index cd57f79..e37faa3 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -156,6 +156,13 @@
 	spin_unlock(&inode->i_lock);
 }
 
+void nfs_invalidate_atime(struct inode *inode)
+{
+	spin_lock(&inode->i_lock);
+	NFS_I(inode)->cache_validity |= NFS_INO_INVALID_ATIME;
+	spin_unlock(&inode->i_lock);
+}
+
 /*
  * Invalidate, but do not unhash, the inode.
  * NB: must be called with inode->i_lock held!