buffer overflow in nds32_elf_lo12_reloc

nds32_elf_lo12_reloc reads the lo reloc word when processing stashed
hi relocs.

	* elf32-nds32.c: Replace bfd_octets_per_byte with OCTETS_PER_BYTE
	throughout file.
	(nds32_elf_lo12_reloc): Sanity check reloc offset.