clocksource/drivers/timer-ti-dm: Convert to devm_platform_ioremap_resource

Use devm_platform_ioremap_resource() to simplify code, which
wraps 'platform_get_resource' and 'devm_ioremap_resource' in a
single helper.

Signed-off-by: Yangtao Li <tiny.windzz@gmail.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20191221173027.30716-4-tiny.windzz@gmail.com