vfio/mdev: Avoid inline get and put parent helpers

As section 15 of Documentation/process/coding-style.rst clearly
describes that compiler will be able to optimize code.

Hence drop inline for get and put helpers for parent.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>