clocksource: tcb_clksrc: sanitize IRQ request

The clock is not unprepared in case of the request IRQ fails.

Also update to request_irq.

Signed-off-by: Gaël PORTAY <gael.portay@gmail.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>