linux-user: correct stat structure in MIPS N32

Simple "hello world" MIPS N32 userland program crashes with segfault due to
incorrectly defined stat structure in QEMU.

Correct "target_stat" definition to match kernel's "stat64" as in MIPS N32
there are only plain "stat" syscalls using 64-bit structure.

Reported-by: Daniel Sanders <daniel.sanders@imgtec.com>
Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
Tested-by: Daniel Sanders <daniel.sanders@imgtec.com>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
