x86-64: Use x86_64_elf_howto_table for standard relocations

For standard relocations, use x86_64_elf_howto_table, instead of calling
elf_x86_64_rtype_to_howto.

	* elf64-x86-64.c (elf_x86_64_tls_transition): Use
	x86_64_elf_howto_table, instead of elf_x86_64_rtype_to_howto.
	(elf_x86_64_convert_load_reloc): Use x86_64_elf_howto_table,
	instead of elf_x86_64_rtype_to_howto, for R_X86_64_PC32.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>