tty: serial: qcom_geni_serial: No need to stop tx/rx on UART shutdown

On a board using qcom_geni_serial I found that I could no longer
interact with kdb if I got a crash after the "agetty" running on the
same serial port was killed.  This meant that various classes of
crashes that happened at reboot time were undebuggable.

Reading through the code, I couldn't figure out why qcom_geni_serial
felt the need to run so much code at port shutdown time.  All we need
to do is disable the interrupt.

After I make this change then a hardcoded kgdb_breakpoint in some late
shutdown code now allows me to interact with the debugger.  I also
could freely close / re-open the port without problems.

Fixes: c4f5287 ("tty: serial: msm_geni_serial: Add serial driver support for GENI based QUP")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20200313134635.1.Icf54c533065306b02b880c46dfd401d8db34e213@changeid
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/qcom_geni_serial.c

@@ -825,17 +825,11 @@ static void get_tx_fifo_size(struct qcom_geni_serial_port *port)
 
 static void qcom_geni_serial_shutdown(struct uart_port *uport)
 {
-	unsigned long flags;
-
 	/* Stop the console before stopping the current tx */
 	if (uart_console(uport))
 		console_stop(uport->cons);
 
 	disable_irq(uport->irq);
-	spin_lock_irqsave(&uport->lock, flags);
-	qcom_geni_serial_stop_tx(uport);
-	qcom_geni_serial_stop_rx(uport);
-	spin_unlock_irqrestore(&uport->lock, flags);
 }
 
 static int qcom_geni_serial_port_setup(struct uart_port *uport)