The clk_disable_unprepare() should be called in the error handling
of clk_get_rate(), fix it.

Fixes: b5b2bdfc ("rtc: st: Add new driver for ST's LPC RTC")
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Link: https://lore.kernel.org/r/20221123014805.1993052-1-cuigaosheng1@huawei.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>