tcmu: fix multiple uio open/close sequences

If the uio device is open and closed multiple times, the
kref count will be off due to tcmu_release getting called
multiple times for each close. This patch integrates
Wenji Tang's patch to add a kref_get on open that now
matches the kref_put done on tcmu_release and adds
a kref_put in tcmu_destroy_device to match the kref_get
done in succesful tcmu_configure_device calls.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Cc: Wenji Tang <tang.wenji@zte.com.cn>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>