rtc: mxc_v2: Add missing clk_disable_unprepare()

The call to clk_disable_unprepare() is left out in the error handling of
devm_rtc_allocate_device. Add it back.

Fixes: 5490a1e0 ("rtc: mxc_v2: fix possible race condition")
Signed-off-by: GUO Zihua <guozihua@huawei.com>
Link: https://lore.kernel.org/r/20221122085046.21689-1-guozihua@huawei.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>