scsi: qla2xxx: Remove unused irq_cmd_count field.

When driver is unloaded, all sessions are torn down, all commmands are
flushed, chip is reset to ensure there is no knowledge of target mode in
ISP. The irq_cmd_count field was used to make sure all commands are
processed on top of that.  The irq_cmd_count is now redundant and not
needed.

Signed-off-by: Quinn Tran <quinn.tran@cavium.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>