vol: Remove redundant vop check in GetVolume

vol: Remove redundant vop check in GetVolume

VAttachVolumeByVp_r (specifically attach_check_vop in attach2) already
handles checking for conflicting vol ops, and gives us VOFFLINE
appropriately. We don't need to check again in GetVolume.

Change-Id: Ibb93d423d3c856dd957a2569412a85698180ff8e
Reviewed-on: http://gerrit.openafs.org/7304
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Tom Keiser <tkeiser@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementix.org>