[SCSI] qla2xxx: Micro optimization in queuecommand handler

Optimized queuecommand handler's to eliminate double head-room checks.
The checks are moved inside the 1st if-loop otherwise you would end up checking twice when there is
enough head room.

Signed-off-by: Chetan Loke <loke.chetan@gmail.com>
Reviewed-by: Andrew Vasquez <andrew.vasquez@qlogic.com>
Reviewed-by: Giridhar Malavali <giridhar.malavali@qlogic.com>
Signed-off-by: Chad Dupuis <chad.dupuis@qlogic.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>