rtc: st-lpc: Add missing clk_disable_unprepare in st_rtc_probe()

rtc: st-lpc: Add missing clk_disable_unprepare in st_rtc_probe()

[ Upstream commit d67c4dbd7f04b51f8e1315f6f7c2f7e009c5496e ]

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

Fixes: c80d01112db1 ("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.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>