bfd/s390: Misc minor fixes.

bfd/s390: Misc minor fixes.

The only non-comment fix here is in the code writing out the 3 fixed
.got.plt entries - it mistakenly put a 64-bit 0 at offsets 8 and 12
instead of 8 and 16.

bfd/ChangeLog:

	* elf32-s390.c (elf_s390_finish_dynamic_symbol): Fix comment.
	* elf64-s390.c (elf_s390x_plt_entry): Fix comment.
	(elf_s390_relocate_section): Fix comment.
	(elf_s390_finish_dynamic_sections): Fix initialization of fixed
	.got.plt entries.