linux-user: fix settime old value location

old_value is the 4th argument of timer_settime(), not the 2nd.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20170119151533.29328-1-bobby.prani@gmail.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>