serial: sh-sci: Fix crash in rx_timer_fn() on PIO fallback

[ Upstream commit 2e948218b7c1262a3830823d6620eb227e3d4e3a ]

When falling back to PIO, active_rx must be set to a different value
than cookie_rx[i], else sci_dma_rx_find_active() will incorrectly find a
match, leading to a NULL pointer dereference in rx_timer_fn() later.

Use zero instead, which is the same value as after driver
initialization.
Signed-off-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>

drivers/tty/serial/sh-sci.c

@@ -1359,7 +1359,7 @@ static int sci_submit_rx(struct sci_port *s, bool port_lock_held)
 		dmaengine_terminate_async(chan);
 	for (i = 0; i < 2; i++)
 		s->cookie_rx[i] = -EINVAL;
-	s->active_rx = -EINVAL;
+	s->active_rx = 0;
 	s->chan_rx = NULL;
 	sci_start_rx(port);
 	if (!port_lock_held)