posix-cpu-timers: Handle SIGEV_NONE timers correctly in timer_set()

posix-cpu-timers: Handle SIGEV_NONE timers correctly in timer_set()

Expired SIGEV_NONE oneshot timers must return 0 nsec for the expiry time in
timer_get(), but the posix CPU timer implementation returns 1 nsec.

Add the missing conditional.

This will be cleaned up in a follow up patch.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>