vfio/mdpy: Fix memory leak of object mdev_state->vconfig

In the case where the call to vfio_register_group_dev fails the error
return path kfree's mdev_state but not mdev_state->vconfig. Fix this
by kfree'ing mdev_state->vconfig before returning.

Addresses-Coverity: ("Resource leak")
Fixes: 437e4136 ("vfio/mdpy: Convert to use vfio_register_group_dev()")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20210622183710.28954-1-colin.king@canonical.comSigned-off-by: Alex Williamson <alex.williamson@redhat.com>

samples/vfio-mdev/mdpy.c

@@ -261,6 +261,7 @@ static int mdpy_probe(struct mdev_device *mdev)
 
 	ret = vfio_register_group_dev(&mdev_state->vdev);
 	if (ret) {
+		kfree(mdev_state->vconfig);
 		kfree(mdev_state);
 		return ret;
 	}