rtc: pcf8563: remove RTC_VL_CLR handling

Remove RTC_VL_CLR handling because it is a disservice to userspace as it
removes the important information that the RTC data is invalid. This may
lead userspace to set an invalid system time later on.

Link: https://lore.kernel.org/r/20191214220259.621996-7-alexandre.belloni@bootlin.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>