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 5fb733d7bd6949e90028efdce8bd528c6ab7cf1e ]

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

Fixes: 76cd9930387e ("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>