[SCSI] qla2xxx: Remove reference to request queue from scsi request block.

srbs used to maintain a reference to the request queue on which
it was enqueued. This is no longer required as the request queue
pointer is now maintained in the scsi host that issues the srb.

Signed-off-by: Anirban Chakraborty <anirban.chakraborty@qlogic.com>
Signed-off-by: Andrew Vasquez <andrew.vasquez@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>