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

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>

drivers/rtc/rtc-st-lpc.c

@@ -238,6 +238,7 @@ static int st_rtc_probe(struct platform_device *pdev)
 
 	rtc->clkrate = clk_get_rate(rtc->clk);
 	if (!rtc->clkrate) {
+		clk_disable_unprepare(rtc->clk);
 		dev_err(&pdev->dev, "Unable to fetch clock rate\n");
 		return -EINVAL;
 	}