MIPS/BFD: Call `mips_elf32_rtype_to_howto' directly with o32

MIPS/BFD: Call `mips_elf32_rtype_to_howto' directly with o32

Call `mips_elf32_rtype_to_howto' directly rather than via the
`->elf_backend_mips_rtype_to_howto' method in the o32 backend,
complementing commit 861fb55ab50a ("Defer allocation of R_MIPS_REL32 GOT
slots"), <https://sourceware.org/ml/binutils/2008-08/msg00096.html>, and
reverting the change to `mips_info_to_howto_rel' originally made with
commit 0a44bf6950b3 ("mips-vxworks support"),
<https://sourceware.org/ml/binutils/2006-03/msg00179.html>.

With `mips_vxworks_rtype_to_howto' gone there is a single backend method
used across all o32 targets, so there in no need for the indirection and
the associated extra cost.  This also makes the o32 backend consistent
with the n32 and n64 backends.

	bfd/
	* elf32-mips.c (mips_info_to_howto_rel): Call
	`mips_elf32_rtype_to_howto' directly rather than via
	`->elf_backend_mips_rtype_to_howto'.