Warnings when compiling

[scemama]

Problem with a const:

In file included from src/trexio_hdf5.h:10,
                 from src/trexio_hdf5.c:6:
src/trexio_hdf5.c:8700:39: warning: passing argument 1 of 'free' discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
 8700 |     if (index_p != index_sparse) FREE(index_p);
      |                                       ^~~~~~~
src/trexio_private.h:12:24: note: in definition of macro 'FREE'
   12 | #define FREE(X) { free(X) ; (X)=NULL; }
      |                        ^
In file included from src/trexio_hdf5.h:14,
                 from src/trexio_hdf5.c:6:
/usr/include/stdlib.h:482:25: note: expected 'void *' but argument is of type 'const void *'
  482 | extern void free (void *__ptr) __THROW;
      |                   ~~~~~~^~~~~