clocksource/drivers/timer-milbeaut: Fix to enable one-shot timer

Fix mlb_set_oneshot_state() to enable one-shot timer.
The function should stop and start a timer, but "start" statement was
dropped. Kick the register to start one-shot timer.

Fixes: b58f28f3 ("clocksource/drivers/timer-milbeaut: Introduce timer for Milbeaut SoCs")
Signed-off-by: Sugaya Taichi <sugaya.taichi@socionext.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>