dm: rtc: Avoid a race in the rtc_reset test

dm: rtc: Avoid a race in the rtc_reset test

Since resetting the RTC on sandbox causes it to read the base time from
the system, we cannot rely on this being unchanged since it was last read.
Allow for a one-second delay.

Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Fixes: https://source.denx.de/u-boot/u-boot/-/issues/4
Reported-by: Bin Meng <bmeng.cn@gmail.com>
Reported-by: Tom Rini <trini@konsulko.com>
Suggested-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: Simon Glass <sjg@chromium.org>