genirq: Make legacy autoprobing work again

Meelis reported the following warning on a quad P3 HP NetServer museum piece:

WARNING: CPU: 3 PID: 258 at kernel/irq/chip.c:244 __irq_startup+0x80/0x100
EIP: __irq_startup+0x80/0x100
irq_startup+0x7e/0x170
probe_irq_on+0x128/0x2b0
parport_irq_probe.constprop.18+0x8d/0x1af [parport_pc]
parport_pc_probe_port+0xf11/0x1260 [parport_pc]
parport_pc_init+0x78a/0xf10 [parport_pc]
parport_parse_param.constprop.16+0xf0/0xf0 [parport_pc]
do_one_initcall+0x45/0x1e0

This is caused by the rewrite of the irq activation/startup sequence which
missed to convert a callsite in the irq legacy auto probing code.

To fix this irq_activate_and_startup() needs to gain a return value so the
pending logic can work proper.

Fixes: c942cee4

 ("genirq: Separate activation and startup")
Reported-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Meelis Roos <mroos@linux.ee>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801301935410.1797@nanos