bfin uart: it will hang when read current y count if not disable dma irq

Add irq disable and enable in bfin_serial_rx_dma_timeout in case of
system hang.

This reverts part of commit 9642dbe7 ("serial: bfin-uart: avoid
dead lock in rx irq handler in smp kernel").
Signed-off-by: Hao Liang <hliang1025@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/bfin_uart.c

@@ -464,6 +464,7 @@ void bfin_serial_rx_dma_timeout(struct bfin_serial_port *uart)
 	int x_pos, pos;
 	unsigned long flags;
 
+	dma_disable_irq_nosync(uart->rx_dma_channel);
 	spin_lock_irqsave(&uart->rx_lock, flags);
 
 	/* 2D DMA RX buffer ring is used. Because curr_y_count and
@@ -496,6 +497,7 @@ void bfin_serial_rx_dma_timeout(struct bfin_serial_port *uart)
 	}
 
 	spin_unlock_irqrestore(&uart->rx_lock, flags);
+	dma_enable_irq(uart->rx_dma_channel);
 
 	mod_timer(&(uart->rx_dma_timer), jiffies + DMA_RX_FLUSH_JIFFIES);
 }