ide: add __ide_default_irq() inline helper

Add __ide_default_irq() inline helper and use it instead of
ide_default_irq() in ide-probe.c and ns87415.c (all host drivers
except IDE PCI ones always setup hwif->irq so it is enough to
check only for I/O bases 0x1f0 and 0x170).

This fixes post-2.6.25 regression since ide_default_irq()
define could shadow ide_default_irq() inline.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>