Never enable update interrupts when the time set on the rtc is invalid.
In that case, also avoid enabling the emulation because it will fail for
the same reason.

Link: https://lore.kernel.org/r/20191021155631.3342-2-alexandre.belloni@bootlin.com
Link: https://lore.kernel.org/r/CA+ASDXMarBG5C1Kz42B9i_iVZ1=i6GgH9Yja2cdmSueKD_As_g@mail.gmail.comReported-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Reported-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>