iscsi-target: Remove unnecessary wait_for_completion in iscsi_get_thread_set

This patch removes an unnecessary wait_for_completion within
iscsi_get_thread_set(), that would wait for 1 second before
trying to obtain an inactive struct iscsi_thread_set from
iscsi_get_ts_from_inactive_list().

Since iscsi_allocate_thread_sets() will already be adding the
newly allocated iscsi_thread_set to the inactive list directly,
there is no need to wait here.

Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>