[SCSI] advansys: Improve interrupt handler

Pass the Scsi_Host to the interrupt handler, rather than polling all
hosts for each interrupt.
Return IRQ_NONE if we didn't handle this interrupt
Don't set the IRQF_DISABLED flag; this is not a fast-executing interrupt
handler.

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>