rtc: ds1307: fix ds1339 wakealarm support

Commit 51ed73eb ("rtc: ds1340: Add support
for trickle charger.") breaks ds1339 wakealarm support by limiting
accessible registers. Fix this.

Fixes: 51ed73eb ("rtc: ds1340: Add support for trickle charger.")
Cc: stable@vger.kernel.org
Signed-off-by: Soeren Moch <smoch@web.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>