fortran: Correct the name of MPI_INTEGER16.

The name of `MPI_INTEGER16` obtained using `MPI_TYPE_GET_NAME`
from Fortran program was incorrect (`MPI_INTEGER8` was obtained)
when `INTEGER*16` is not supported by a compiler.

This bug affects only the Fortran binding because `MPI_INTEGER16`
is not defined in `mpi.h` if a compiler does not support it.

(cherry picked from commit open-mpi/ompi@722e898)

Author: kawashima-fj

ompi/datatype/ompi_datatype_module.c

@@ -258,7 +258,7 @@ ompi_predefined_datatype_t ompi_mpi_integer8 =       OMPI_DATATYPE_INIT_UNAVAILA
 #if OMPI_HAVE_FORTRAN_INTEGER16
 ompi_predefined_datatype_t ompi_mpi_integer16 =      OMPI_DATATYPE_INIT_PREDEFINED_BASIC_TYPE_FORTRAN (INT, INTEGER16, OMPI_SIZEOF_FORTRAN_INTEGER16, OMPI_ALIGNMENT_FORTRAN_INTEGER16, OMPI_DATATYPE_FLAG_DATA_INT);
 #else
-ompi_predefined_datatype_t ompi_mpi_integer16 =      OMPI_DATATYPE_INIT_UNAVAILABLE (INTEGER8, OMPI_DATATYPE_FLAG_DATA_FORTRAN | OMPI_DATATYPE_FLAG_DATA_INT);
+ompi_predefined_datatype_t ompi_mpi_integer16 =      OMPI_DATATYPE_INIT_UNAVAILABLE (INTEGER16, OMPI_DATATYPE_FLAG_DATA_FORTRAN | OMPI_DATATYPE_FLAG_DATA_INT);
 #endif
 
 /*