Detach the ubi device of rootfs

[Rock Lee]

> Why do you think you need to detach upon reboot?
> UBI and UBIFS are designed to face power-cuts at any time.
> Although, sane setups with initramfs/systemd unmount also the rootfs
> upon reboot.
>

When reboot, UBIFS will be remount as read-only, from the filesystem
part, it is safe, because there is no data write to it.  I see ubi
background thread will exit when ubi detach, and there would no
scrubing anymore, I am sure reboot after detach is safe enough in UBI
layer. I am just curious what will happen when reboot the system while
ubi is scrubing. Will it damage the flash if this situation happens a
lot?

Thanks
-- 
Cheers,
Rock