[SCSI] aha1542: minor irq handler cleanups
- where the 'irq' function argument is known never to be used, rename
it to 'dummy' to make this more obvious
- replace per-irq lookup functions and tables with a direct reference
to data object obtained via 'dev_id' function argument, passed from
request_irq()
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
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