serial: sh-sci: Don't kick tx in sci_er_interrupt() when using DMA

If CONFIG_SERIAL_SH_SCI_DMA is enabled, the driver doesn't enable TIE
on SCIF or HSCIF. However, this driver may call sci_tx_interrupt()
in sci_er_interrupt(). After that, the driver cannot care of the
interrupt, and then "irq 109: nobody cared" happens on r8a7791/koelsch
board. This patch fixes the issue.
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
[geert] Keep kicking tx when using PIO
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sh-sci.c

@@ -1011,7 +1011,8 @@ static irqreturn_t sci_er_interrupt(int irq, void *ptr)
 	sci_clear_SCxSR(port, SCxSR_ERROR_CLEAR(port));
 
 	/* Kick the transmission */
-	sci_tx_interrupt(irq, ptr);
+	if (!s->chan_tx)
+		sci_tx_interrupt(irq, ptr);
 
 	return IRQ_HANDLED;
 }