ARM: OMAP1: ams-delta: Fix impossible .irq < 0

Since the very beginning, unsigned int .irq member of struct
plat_serial8250_port introduced by commit eff443df679e ("OMAP1:
AMS_DELTA: add modem support") was statically initialized to a negative
value -EINVAL.  Moreover, commit 0812db943748 ("ARM: OMAP1: ams-delta:
assign MODEM IRQ from GPIO descriptor") has introduced some new code
which checks for that member carrying a negative value which is
impossible.

Use IRQ_NOTCONNECTED instead of -EINVAL. Also, drop the valueless check
and let the modem device be registered regardless of .irq value, and
the value handled by "serial8250" driver.

Fixes: 0812db943748 ("ARM: OMAP1: ams-delta: assign MODEM IRQ from GPIO descriptor")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Acked-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap1/board-ams-delta.c

@@ -765,7 +765,7 @@ static struct plat_serial8250_port ams_delta_modem_ports[] = {
 	{
 		.membase	= IOMEM(MODEM_VIRT),
 		.mapbase	= MODEM_PHYS,
-		.irq		= -EINVAL, /* changed later */
+		.irq		= IRQ_NOTCONNECTED, /* changed later */
 		.flags		= UPF_BOOT_AUTOCONF,
 		.irqflags	= IRQF_TRIGGER_RISING,
 		.iotype		= UPIO_MEM,
@@ -856,8 +856,7 @@ static int __init modem_nreset_init(void)
 
 
 /*
- * This function expects MODEM IRQ number already assigned to the port
- * and fails if it's not.
+ * This function expects MODEM IRQ number already assigned to the port.
  * The MODEM device requires its RESET# pin kept high during probe.
  * That requirement can be fulfilled in several ways:
  * - with a descriptor of already functional modem_nreset regulator
@@ -880,9 +879,6 @@ static int __init ams_delta_modem_init(void)
 	if (!machine_is_ams_delta())
 		return -ENODEV;
 
-	if (ams_delta_modem_ports[0].irq < 0)
-		return ams_delta_modem_ports[0].irq;
-
 	omap_cfg_reg(M14_1510_GPIO2);
 
 	/* Initialize the modem_nreset regulator consumer before use */