MIPS: Fix inconsistancy of __NR_Linux_syscalls value

Originally, __NR_O32_Linux_syscalls, __NR_N32_Linux_syscalls and
__NR_64_Linux_syscalls have the same values as __NR_Linux_syscalls in
corresponding ABIs. But after commit 367f0b50 (MIPS: Wire up
renameat2 syscall) they are not the same. I think this is incorrect and
need a fix.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Cc: John Crispin <john@phrozen.org>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: linux-mips@linux-mips.org
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/6987/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>