9p: drop broken unused error path from p9_conn_create()

Post p9_fd_poll() error path which checks m->poll_waddr[i] for PTR_ERR
value has the following problems.

* It's completely unused.  Error value is set iff NULL @wait_address
  has been specified to p9_pollwait() which is guaranteed not to
  happen.

* It dereferences @m after deallocating it (introduced by 571ffeaf and
  spotted by Raja R Harinath.

* It returned the wrong value on error.  It should return
  poll_waddr[i] but it returnes poll_waddr (introduced by 571ffeaf

).

* p9_mux_poll_stop() doesn't handle PTR_ERR value.  It will try to
  operate on the PTR_ERR value as if it's a normal pointer and cause
  oops.

As the error path is bogus in the first place, there's no reason to
hold onto it.  Kill it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Raja R Harinath <harinath@hurrynot.org>