be2iscsi: Cleanup processing of BMBX completion

Remove confusingly named be_mcc_compl_is_new and be_mcc_compl_use
functions in processing of BMBX. Rearrange beiscsi_process_mbox_compl
function.

Signed-off-by: Jitendra Bhivare <jitendra.bhivare@broadcom.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>