pml/cm: Fix datatype offset in isend

Previously due to the MTL avoiding entering
the convertor for optimization, data offsetting
was not properly calculated. In order to fix this,
the datatype offset was moved from mca_pml_cm_send
into ompi_mtl_datatype_pack. This change was not
incorporated into the MCA_PML_CM_SEND_REQUEST_INIT_COMMON
macro and thus offset would be added twice during isend.

Signed-off-by: William Zhang <wilzhang@amazon.com>

Author: wckzhang

ompi/mca/pml/cm/pml_cm_sendreq.h

@@ -246,7 +246,7 @@ do {                                                                    \
         /* Sets CONVERTOR_ACCELERATOR flag if device buffer */                   \
         opal_convertor_prepare_for_send(                            \
             &req_send->req_base.req_convertor,                      \
-            &datatype->super, count, (unsigned char*)buf + datatype->super.true_lb); \
+            &datatype->super, count, (unsigned char*)buf); \
     } else {                                                            \
         MCA_PML_CM_SWITCH_ACCELERATOR_CONVERTOR_OFF(flags, datatype, count);   \
         opal_convertor_copy_and_prepare_for_send(                       \