clocksource/drivers/sun5i: Use of_io_request_and_map()

of_iomap doesn't do a request_mem_region() on the memory area
defined in the DT it maps. Switch to of_io_request_and_map() to
make sure we're the only users.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1427796746-373-3-git-send-email-daniel.lezcano@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>