rtc: rv8803: avoid clearing RV8803_FLAG_V2F in RTC_VL_CLR

Stop clearing RV8803_FLAG_V2F in RTC_VL_CLR 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/20191214220259.621996-15-alexandre.belloni@bootlin.com


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