power: supply: ab8500: stop using getnstimeofday64()

getnstimeofday64() is deprecated in favor of the ktime_get() family.

The direct replacement would be ktime_get_real_ts64(), but we only need
the seconds value, and it seems better to use boottime than real time
to avoid unexpected behavior with a concurrent settimeofday().

ktime_get_seconds() might also work, but it seems better to use
boottime than monotonic time since I assume that the charging
process continues during suspend.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>