[SCSI] qla2xxx: Remove unused member (list) from srb_t structure.

This change reduces by as much as 16% the memory footprint for
each allocated sbr_t structure requested from the mempool.

Signed-off-by: Andrew Vasquez <andrew.vasquez@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>