Do not set the system power-off callback and omap power-off rtc pointer
until we're done setting up our device to avoid leaving stale pointers
around after a late probe error.
Fixes: 97ea1906b3c2 ("rtc: omap: Support ext_wakeup configuration")
Cc: stable <stable@xxxxxxxxxxxxxxx> # 4.9
Cc: Marcin Niestroj <m.niestroj@xxxxxxxxxxxxxxxx>
Cc: Tony Lindgren <tony@xxxxxxxxxxx>
Signed-off-by: Johan Hovold <johan@xxxxxxxxx