rtc: stm32: use 0 instead of ~PWR_CR_DBP in regmap_update_bits

rtc: stm32: use 0 instead of ~PWR_CR_DBP in regmap_update_bits

Using the ~ operator on a BIT() constant results in a large 'unsigned long'
constant that won't fit into an 'unsigned int' function argument on 64-bit
architectures, resulting in a harmless build warning in x86 allmodconfig:

drivers/rtc/rtc-stm32.c: In function 'stm32_rtc_probe':
drivers/rtc/rtc-stm32.c:651:51: error: large integer implicitly truncated to unsigned type [-Werror=overflow]
  regmap_update_bits(rtc->dbp, PWR_CR, PWR_CR_DBP, ~PWR_CR_DBP);

As PWR_CR_DBP mask prevents other bits to be cleared, replace all
~PWR_CR_DBP by 0.

Fixes: 4e64350f42e2 ("rtc: add STM32 RTC driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>