Fixed Regression in NFS Direct I/O path

A typo, introduced by commit f11ac8d, in the nfs_direct_write()
routine causes writes with O_DIRECT set to fail with a ENOMEM error.

Found-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve Dickson <steved@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/direct.c

@@ -873,7 +873,7 @@ static ssize_t nfs_direct_write(struct kiocb *iocb, const struct iovec *iov,
 	dreq->inode = inode;
 	dreq->ctx = get_nfs_open_context(nfs_file_open_context(iocb->ki_filp));
 	dreq->l_ctx = nfs_get_lock_context(dreq->ctx);
-	if (dreq->l_ctx != NULL)
+	if (dreq->l_ctx == NULL)
 		goto out_release;
 	if (!is_sync_kiocb(iocb))
 		dreq->iocb = iocb;