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

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 <[email protected]>
Signed-off-by: Janusz Krzysztofik <[email protected]>
Acked-by: Aaro Koskinen <[email protected]>
Signed-off-by: Tony Lindgren <[email protected]>