[MIPS] The o32 fstatat syscall behaves differently on 32 and 64 bit kernels

While working on a glibc patch to support the fstatat() functions[1],
I noticed that the o32 implementation behaves differently on 32-bit and
64-bit kernels; the former provides a stat64 while the latter provides
a plain (o32) stat.  I think the former is what's intended, as there is
no separate fstatat64.  It's also what x86 does.

I think this is just a case of a compat too far.

[1] I've seen Khem's patch, but I don't think it's right.

Signed-off-by: Richard Sandiford <richard@codesourcery.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>