tty: serial: fsl_lpuart: make coverity happy

Coverity reports the following:

  var_compare_op: Comparing chan to null implies that chan might be null.

  1234        if (chan)
  1235                dmaengine_terminate_all(chan);
  1236

  Dereference after null check (FORWARD_NULL)
  var_deref_op: Dereferencing null pointer chan.

  1237        dma_unmap_sg(chan->device->dev, &sport->rx_sgl, 1, DMA_FROM_DEVICE);

Technically, this is correct. But lpuart_dma_rx_free() is guarded by
lpuart_dma_rx_use which is only true if there is a dma channel, see
lpuart_rx_dma_startup(). In any way, this looks bogus. So remove
the superfluous "if (chan)" check and make coverity happy.

Fixes: a092ab25 ("tty: serial: fsl_lpuart: fix DMA mapping")
Signed-off-by: NMichael Walle <michael@walle.cc>
Reported-by: NColin Ian King <colin.king@canonical.com>
Acked-by: NJiri Slaby <jslaby@suse.cz>
Reviewed-by: NFabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20200403174942.9594-1-michael@walle.ccSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/fsl_lpuart.c

@@ -1231,9 +1231,7 @@ static void lpuart_dma_rx_free(struct uart_port *port)
 					struct lpuart_port, port);
 	struct dma_chan *chan = sport->dma_rx_chan;
 
-	if (chan)
-		dmaengine_terminate_all(chan);
-
+	dmaengine_terminate_all(chan);
 	dma_unmap_sg(chan->device->dev, &sport->rx_sgl, 1, DMA_FROM_DEVICE);
 	kfree(sport->rx_ring.buf);
 	sport->rx_ring.tail = 0;