mips: fix n32 compat_ipc_parse_version

While reading through the sysvipc implementation, I noticed that the n32
semctl/shmctl/msgctl system calls behave differently based on whether
o32 support is enabled or not: Without o32, the IPC_64 flag passed by
user space is rejected but calls without that flag get IPC_64 behavior.

As far as I can tell, this was inadvertently changed by a cleanup patch
but never noticed by anyone, possibly nobody has tried using sysvipc
on n32 after linux-3.19.

Change it back to the old behavior now.

Fixes: 78aaf956 ("MIPS: Compat: Fix build error if CONFIG_MIPS32_COMPAT but no compat ABI.")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: stable@vger.kernel.org # 3.19+