s390/vfio-ap: Fix memory allocation for mdev_types array

The vfio-ap crypto driver fails to allocate memory for an array of
pointers used to pass supported mdev types to mdev_register_parent().

Since we only support a single mdev type, the fix is to allocate a
single entry in the ap_matrix_dev->mdev_types array.

Link: https://lore.kernel.org/r/20221021145905.15100-1-jjherne@linux.ibm.com
Fixes: da44c340 ("vfio/mdev: simplify mdev_type handling")
Cc: stable@vger.kernel.org
Cc: Tony Krowiak <akrowiak@linux.ibm.com>
Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Jason J. Herne <jjherne@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

drivers/s390/crypto/vfio_ap_private.h

@@ -52,7 +52,7 @@ struct ap_matrix_dev {
 	struct mutex guests_lock; /* serializes access to each KVM guest */
 	struct mdev_parent parent;
 	struct mdev_type mdev_type;
-	struct mdev_type *mdev_types[];
+	struct mdev_type *mdev_types[1];
 };
 
 extern struct ap_matrix_dev *matrix_dev;