MIPS: Fix addend handling with rela R_MIPS16_GOT16 and R_MICROMIPS_GOT16

In rela howtos these relocations should not be using
_bfd_mips_elf_got16_reloc.  That special function is for extracting
addends from section contents, and only for that (ie. it doesn't
subtract gp).  Make these rela howtos like the corresponding
R_MIPS_GOT16 rela howto.

	* elf64-mips.c (mips16_elf64_howto_table_rela <R_MIPS16_GOT16>):
	Use _bfd_mips_elf_generic_reloc.
	(micromips_elf64_howto_table_rela <R_MICROMIPS_GOT16>): Likewise.
	* elfn32-mips.c (elf_mips16_howto_table_rela <R_MIPS16_GOT16>):
	Likewise.
	(elf_micromips_howto_table_rela <R_MICROMIPS_GOT16>): Likewise.