[ide] amd74xx: don't probe for IRQs

From: Nicholas Reilly <nreilly@magma.ca>

I have a Shuttle SN41G2 and the secondary IDE channel alternates between
IRQ 15 (correct) and IRQ 7 (causing failures accessing the DVD+-RW which is
master, no slave and also messing with the parallel port if it is enabled)
on each boot.  This is running ACPI and APIC on 2.6.5, 2.6.7 and 2.6.8. 
dmesg, dmidecode and /proc/acpi/dsdt are all identical (apart from dmesg
printing of IRQ and errors it causes) regardless of whether it decides to
go on 7 or 15.  It is now running the latest BIOS, earlier BIOS did the
same.

bart: IRQ auto-detection sometimes fails and gets "screaming" IRQ
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@elka.pw.edu.pl>

drivers/ide/pci/amd74xx.c

@@ -416,6 +416,9 @@ static void __init init_hwif_amd74xx(ide_hwif_t *hwif)
 {
 	int i;
 
+	if (!hwif->irq)
+		hwif->irq = hwif->channel ? 15 : 14;
+
 	hwif->autodma = 0;
 
 	hwif->tuneproc = &amd74xx_tune_drive;