Always pass a valid section header offset to elf_parse_notes

Always pass a valid section header offset to elf_parse_notes

_bfd_elf_make_section_from_shdr calls elf_parse_notes with an offset
of -1.  This argument is used to calculate Elf_Internal_Note.descpos,
which ends up set to a positive but meaningless value.  This commit
updates _bfd_elf_make_section_from_shdr to pass the correct offset to
elf_parse_notes, making Elf_Internal_Note.descpos correct in all cases.

bfd/ChangeLog:

	* elf.c (_bfd_elf_make_section_from_shdr): Pass offset to
	elf_parse_notes.