ubifs: allow encryption ioctls in compat mode

The ubifs encryption ioctls did not work when called by a 32-bit program
on a 64-bit kernel.  Since 'struct fscrypt_policy' is not affected by
the word size, ubifs just needs to allow these ioctls through, like what
ext4 and f2fs do.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Richard Weinberger <richard@nod.at>