readelf: Fix use-after-free ebl pointer issue

readelf: Fix use-after-free ebl pointer issue

With -flto gcc 13 sees that we use the ebl pointer after closing and
freeing it.

In function ‘process_elf_file’,
    inlined from ‘process_dwflmod’ at readelf.c:818:3:
readelf.c:1070:6: error: pointer ‘ebl_18’ used after ‘free’ [-Werror=use-after-free]
 1070 |   if (pure_ebl != ebl)
      |      ^
In function ‘ebl_closebackend’,
    inlined from ‘process_elf_file’ at readelf.c:1068:3,
    inlined from ‘process_dwflmod’ at readelf.c:818:3:
../libebl/eblclosebackend.c:47:7: note: call to ‘free’ here
   47 |       free (ebl);
      |       ^

Fix by only calling ebl_closebackend after using it in the comparison.

Signed-off-by: Mark Wielaard <mark@klomp.org>