6093 zfsctl_shares_lookup should only VN_RELE() on zfs_zget() success

Reviewed by: Gordon Ross <gwr@nexenta.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Dan McDonald <danmcd@omniti.com>

illumos/illumos-gate@0f92170f1ec2737ee5a0e51b5f74093904811452