timerfd: Setup @ticks only if nonzero

If @ticks is zero the kernel returns error
because on creation the @ticks is already zero,
so simply setup @ticks if real value present.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>