Bluetooth: Controller: Explicit ticker worker trigger on expire in past

When ticks_to_expire is in the past, i.e. ticks_to_expire is
0, perform an explicit trigger of ticker worker instead of
setting up the compare which delays the trigger by the
minimum ticks offset margin. The changes reduce latencies
of the O(n) ticker_resolve_collision by upto the minimum
ticks offset margin (3 for nRF SoCs) for each resolution.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>