rtc: stm32: Use NOIRQ_SYSTEM_SLEEP_PM_OPS()

rtc: stm32: Use NOIRQ_SYSTEM_SLEEP_PM_OPS()

After the switch to SET_NOIRQ_SYSTEM_SLEEP_PM_OPS() and a subsequent
fix, stm32_rtc_{suspend,resume}() are unused when CONFIG_PM_SLEEP is not
set because SET_NOIRQ_SYSTEM_SLEEP_PM_OPS() is a no-op in that
configuration:

  drivers/rtc/rtc-stm32.c:904:12: error: 'stm32_rtc_resume' defined but not used [-Werror=unused-function]
    904 | static int stm32_rtc_resume(struct device *dev)
        |            ^~~~~~~~~~~~~~~~
  drivers/rtc/rtc-stm32.c:894:12: error: 'stm32_rtc_suspend' defined but not used [-Werror=unused-function]
    894 | static int stm32_rtc_suspend(struct device *dev)
        |            ^~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors

The non-"SET_" version of this macro, NOIRQ_SYSTEM_SLEEP_PM_OPS(), is
designed to handle this situation by only assigning the callbacks when
CONFIG_PM_SLEEP is set while allowing the functions to appear used to
the compiler. Switch to that macro to resolve the warnings. There is no
functional change with this, as SET_NOIRQ_SYSTEM_SLEEP_PM_OPS() is
defined using NOIRQ_SYSTEM_SLEEP_PM_OPS() when CONFIG_PM_SLEEP is set.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20230815-rtc-stm32-unused-pm-funcs-v1-1-82eb8e02d903@kernel.org
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>