[SCSI] qla2xxx: Fix qla24xx revision check while enabling interrupts.

Since we enable interrupts before initializing the firmware, use the chip
revision from PCI config space directly to perform the chip revision check.
Also remove the unnecessary firmware attributes test.

Signed-off-by: Chad Dupuis <chad.dupuis@qlogic.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>