With cmwq, there's no reason to use a dedicated workqueue in trans_fd.
Drop p9_mux_wq and use system_wq instead. The used work items are
already sync canceled in p9_conn_destroy() and doesn't require further
synchronization.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Eric Van Hensbergen <ericvh@gmail.com> Cc: Ron Minnich <rminnich@sandia.gov> Cc: Latchesar Ionkov <lucho@ionkov.net> Cc: v9fs-developer@lists.sourceforge.net