scsi: g_NCR5380: Fix automatic IRQ on HP C2502 cards

When IRQ_AUTO is used, the interrupt for HP C2502 cards gets disabled.
Fix this by programming the card for a suitable free irq. The code for
the free irq search comes from ALSA.

Also allow IRQ 9 to work (it aliases to IRQ 2 on the card), as per
Ondrej Zary's patch.

Suggested-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Tested-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>