Fixed integer size to match what ex_get_block() requires

With UBSan, many Exodus-related tests failed with:

VTK/ThirdParty/exodusII/vtkexodusII/src/ex_get_block.c:65:7: runtime error: store to misaligned address 0x7ff7bdd396c4 for type 'int64_t' (aka 'long long'), which requires 8 byte alignment

And indeed ex_get_block(), despite taking void*, casts that paramater to int64_t*, and thus it actually needs to be an int64_t.

I guess this only worked at all previously since most CPUs are little endian these days.