pinctrl: amd: use higher precision for 512 RtcClk

pinctrl: amd: use higher precision for 512 RtcClk

RTC is 32.768kHz thus 512 RtcClk equals 15625 usec. The documentation
likely has dropped precision and that's why the driver mistakenly took
the slightly deviated value.

Cc: stable@vger.kernel.org
Reported-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Suggested-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Coiby Xu <coiby.xu@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/linux-gpio/2f4706a1-502f-75f0-9596-cc25b4933b6c@redhat.com/
Link: https://lore.kernel.org/r/20201105231912.69527-3-coiby.xu@gmail.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>