UBI ioctl's do not work when running 64-bit kernel and 32-bit
user-land. Fix this by adding the compat_ioctl method.
Also, UBI serializes all ioctls, so more than one ioctl at a time
is not a problem. Amd UBI does not seem to depend on anything else,
so use unlocked_ioctl instead of ioctl (no BKL needed).