clocksource/drivers/exynos_mct: Clear timer interrupt when shutdown

When shutting down the timer, ensure that after we have stopped the
timer any pending interrupts are cleared. This fixes a problem when
suspending, as interrupts are disabled before the timer is stopped,
so the timer interrupt may still be asserted, preventing the system
entering a low power state when the wfi is executed.

Signed-off-by: Stuart Menefy <stuart.menefy@mathembedded.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: <stable@vger.kernel.org> # v4.3+
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>