objstore: use vol's vdev reference when needed
objstore: use vol's vdev reference when needed

We don't need to lock since the vdev reference doesn't change throughout the
lifetime of the volume.

Signed-off-by: Josef 'Jeff' Sipek <a620f141433c70aa9e43778305a6c68cbfadfb25@josefsipek.net>

jeffpc/nx01