Revert "serial: pl011: Fix DMA ->flush_buffer()"

This reverts commit 8764ed5 which is
commit f6a1964 upstream.

It's being reverted becuase it causes build errors:

drivers/tty/serial/amba-pl011.c:687:2: error:
  implicit declaration of function ‘dmaengine_terminate_async’;
  did you mean ‘dmaengine_terminate_all’?
    [-Werror=implicit-function-declaration]

Change-Id: I968b66a26997009690fb1f478e225384412f0c01
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Author: Lee Jones

drivers/tty/serial/amba-pl011.c

@@ -684,8 +684,10 @@ __acquires(&uap->port.lock)
 	if (!uap->using_tx_dma)
 		return;
 
-	dmaengine_terminate_async(uap->dmatx.chan);
-
+	/* Avoid deadlock with the DMA engine callback */
+	spin_unlock(&uap->port.lock);
+	dmaengine_terminate_all(uap->dmatx.chan);
+	spin_lock(&uap->port.lock);
 	if (uap->dmatx.queued) {
 		dma_unmap_sg(uap->dmatx.chan->device->dev, &uap->dmatx.sg, 1,
 			     DMA_TO_DEVICE);