serial: sh-sci: Stop dmaengine transfer in sci_stop_tx()

Stop dmaengine transfer in sci_stop_tx(). Otherwise, the following
message is possible output when system enters suspend and while
transferring data, because clearing TIE bit in SCSCR is not able to
stop any dmaengine transfer.

    sh-sci e6550000.serial: ttySC1: Unable to drain transmitter

Note that this driver has already used some #ifdef in the .c file
so that this patch also uses #ifdef to fix the issue. Otherwise,
build errors happens if the CONFIG_SERIAL_SH_SCI_DMA is disabled.

Fixes: 73a19e4c ("serial: sh-sci: Add DMA support.")
Cc: <stable@vger.kernel.org> # v4.9+
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20210610110806.277932-1-yoshihiro.shimoda.uh@renesas.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sh-sci.c

@@ -611,6 +611,14 @@ static void sci_stop_tx(struct uart_port *port)
 	ctrl &= ~SCSCR_TIE;
 
 	serial_port_out(port, SCSCR, ctrl);
+
+#ifdef CONFIG_SERIAL_SH_SCI_DMA
+	if (to_sci_port(port)->chan_tx &&
+	    !dma_submit_error(to_sci_port(port)->cookie_tx)) {
+		dmaengine_terminate_async(to_sci_port(port)->chan_tx);
+		to_sci_port(port)->cookie_tx = -EINVAL;
+	}
+#endif
 }
 
 static void sci_start_rx(struct uart_port *port)