serial: pch: Fix PCI device refcount leak in pch_request_dma()

As comment of pci_get_slot() says, it returns a pci_device with its
refcount increased. The caller must decrement the reference count by
calling pci_dev_put().

Since 'dma_dev' is only used to filter the channel in filter(), we can
call pci_dev_put() before exiting from pch_request_dma(). Add the
missing pci_dev_put() for the normal and error path.

Fixes: 3c6a483 ("Serial: EG20T: add PCH_UART driver")
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Link: https://lore.kernel.org/r/20221122114559.27692-1-wangxiongfeng2@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/pch_uart.c

@@ -694,6 +694,7 @@ static void pch_request_dma(struct uart_port *port)
 	if (!chan) {
 		dev_err(priv->port.dev, "%s:dma_request_channel FAILS(Tx)\n",
 			__func__);
+		pci_dev_put(dma_dev);
 		return;
 	}
 	priv->chan_tx = chan;
@@ -710,13 +711,16 @@ static void pch_request_dma(struct uart_port *port)
 			__func__);
 		dma_release_channel(priv->chan_tx);
 		priv->chan_tx = NULL;
+		pci_dev_put(dma_dev);
 		return;
 	}
 
 	/* Get Consistent memory for DMA */
 	priv->rx_buf_virt = dma_alloc_coherent(port->dev, port->fifosize,
 				    &priv->rx_buf_dma, GFP_KERNEL);
 	priv->chan_rx = chan;
+
+	pci_dev_put(dma_dev);
 }
 
 static void pch_dma_rx_complete(void *arg)