clocksource/drivers/timer-ti-dm: Fix missing clk_disable_unprepare in dmtimer_systimer_init_clock()

If clk_get_rate() fails which is called after clk_prepare_enable(),
clk_disable_unprepare() need be called in error path to disable the
clock in dmtimer_systimer_init_clock().

Fixes: 52762fbd ("clocksource/drivers/timer-ti-dm: Add clockevent and clocksource support")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20221029114427.946520-1-yangyingliang@huawei.com


Signed-off-by: Daniel Lezcano <daniel.lezcano@kernel.org>