linux-phytec-ti

9P: Fix race in p9_write_work()

See previous commit about p9_read_work() for details.

This fixes a similar race between p9_write_work() and p9_poll_mux()

Signed-off-by: Simon Derr <simon.derr@bull.net>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>