rtc: stm32: remove __exit annotation on remove callback

The remove function can be called at runtime for a manual 'unbind'
operation and must not be left out from a built-in driver, as kbuild
complains:

`stm32_rtc_remove' referenced in section `.data.stm32_rtc_driver' of drivers/rtc/rtc-stm32.o: defined in discarded section `.exit.text' of drivers/rtc/rtc-stm32.o

This removes the extraneous annotation.

Fixes: 4e64350f ("rtc: add STM32 RTC driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

drivers/rtc/rtc-stm32.c

@@ -657,7 +657,7 @@ static int stm32_rtc_probe(struct platform_device *pdev)
 	return ret;
 }
 
-static int __exit stm32_rtc_remove(struct platform_device *pdev)
+static int stm32_rtc_remove(struct platform_device *pdev)
 {
 	struct stm32_rtc *rtc = platform_get_drvdata(pdev);
 	unsigned int cr;