libertas_tf: Remove create_workqueue

alloc_workqueue replaces deprecated create_workqueue().

A dedicated workqueue has been used since the workitem (viz
&priv->cmd_work per priv, which maps to lbtf_cmd_work) is involved in
actual command processing and may be used on a memory reclaim path.
The workitems require forward progress under memory pressure and hence,
WQ_MEM_RECLAIM has been set. Since there are only a fixed number of work
items, explicit concurrency limit is unnecessary here.

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>