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 361c6ed6 ("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>