Well, nothing we can do about it.

But, just remember that sometime the process time on apple based device (and others platform as well) didn't as reliable.

The "1 minute remaining" installation message that took 2 hours to finish.

The Mail app sending message that tell "34 minute remaining" but actually it's sent and we got bewildered when receiving reply of our message that "didn't" sent yet.  

So, be patient, :)

You could soft reset it, power-off and then turn it on again, or another reset, press home button and power button at same time until the device turned off and boot by itself.

Got some solution from discussions.apple.com, flip the airplane switch to on, it'll gave the error message, flip it to off again, and all is well, the iCloud drive status is on. Weird, not pretty solution, but worked, so no problem for me.

But that won't guarantee the problem is solved for everyone, :)

Some succeed by using it and some didn't.

The alternative is, again, be patient, :)