rtc: ds1685: arm the wake-up alarm at power-off only if an alarm is set

ds1685_rtc_poweroff() always sets WIE. The wake-up alarm then compares
the time-of-day and date alarm registers, which hold whatever was last
written to them, and a match powers the machine straight back on.

Set WIE only when AIE is set in Control B, and clear it otherwise.

Fixes: aaaf5fbf56f1 ("rtc: add driver for DS1685 family of real time clocks")
Signed-off-by: Imre Kaloz <kaloz@kernel.org>
Acked-by: Joshua Kinard <linux@kumba.dev>
Link: https://patch.msgid.link/20261013120208.11268-2-kaloz@kernel.org
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>