vfio/mdev: update outdated comment

vfio/mdev: update outdated comment

The function add_mdev_supported_type() was renamed mdev_type_add() in
commit da44c340c4fe ("vfio/mdev: simplify mdev_type handling").
Update the comment accordingly.

Note that just as mdev_type_release() now states that its put pairs
with the get in mdev_type_add(), mdev_type_add() already stated that
its get pairs with the put in mdev_type_release().

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
Reviewed-by: Kirti Wankhede <kwankhede@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20251230164113.102604-1-Julia.Lawall@inria.fr
Signed-off-by: Alex Williamson <alex@shazbot.org>