[SCSI] sym53c8xx: Make interrupt handler capable of returning IRQ_NONE

Make sym_interrupt return an irqreturn_t instead of void, and take a
Scsi_Host instead of a sym_hcb.  Pass the Scsi_Host to the interrupt
handler instead of the sym_hcb.  Rename the host_data to sym_data.
Keep a pci_dev pointer in the sym_data.  Rename the Scsi_Host from
instance to shost.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>