rtc: ds1685: actually spin forever in poweroff path

rtc: ds1685: actually spin forever in poweroff path

objtool reports the following warning:

  drivers/rtc/rtc-ds1685.o: warning: objtool: ds1685_rtc_poweroff() falls through to next function ds1685_rtc_work_queue()

Similar to commit c511a1a97298 ("rtc: ds1685: actually spin forever in
poweroff error path"), there's another unreachable() annotation which is
actually reachable, which we missed the first time.

Actually spin forever to be consistent with the comment and to make the
unreachable() annotation guaranteed to be unreachable.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>