hdf5_ep

[svn-r4107] 
Purpose:
    Bug fix
Description:
    One of the function calls (H5Sget_simple_extent_dims) used parameter with
    the wrong type. That caused compilation errors on T3E.
Solution:
    Used NULL since that argument is optional and was never used.
Platforms tested:
    T3E(mcurie) and IRIX64 (modi4)