readelf: Use section_name instead of elf_strptr in print_debug_frame_section

readelf: Use section_name instead of elf_strptr in print_debug_frame_section

All other print_debug_* functions use section_name (ebl, shdr) to get
the current section name. Be consistent and use the same method in
print_debug_frame_section to make static analyzers happy who might
think elf_strptr can return NULL in this case.

      * src/readelf.c (print_debug_frame_section): Use section_name
      instead of elf_strptr to get the section name.

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