helper: Cast to 'int' explicitly in MPI count arguments
helper: Cast to 'int' explicitly in MPI count arguments

Without an explicit conversion some compilers warn:

    conversion from 'size_t' to 'int', possible loss of data

In these cases we do not expect the size to be beyond 2^31.

ornladios/ADIOS2,ornladios/ADIOS2,JasonRuonanWang/ADIOS2,ornladios/ADIOS2,ornladios/ADIOS2,JasonRuonanWang/ADIOS2,JasonRuonanWang/ADIOS2,JasonRuonanWang/ADIOS2,JasonRuonanWang/ADIOS2,ornladios/ADIOS2