armv8crypto: fix AES-XTS regression introduced by ed9b7f44

Initialization of the XTS key schedule was accidentally dropped
when adding AES-GCM support so all-zero schedule was used instead.
This rendered previously created GELI partitions unusable.
This change restores proper XTS key schedule initialization.

Reported by: Peter Jeremy <peter@rulingia.com>
MFC after: immediately
Approved by: re (gjb)

(cherry picked from commit 748be78e60ccc4a26325a636347debb1f7e6749b)