9p: fix use after free

On 7/22/07, Adrian Bunk <bunk@stusta.de> wrote:
     The Coverity checker spotted the following use-after-free
     in net/9p/mux.c:

     <--  snip  -->

     ...
     struct p9_conn *p9_conn_create(struct p9_transport *trans, int msize,
                                         unsigned char *extended)
     {
     ...
             if (!m->tagpool) {
                     kfree(m);
                     return ERR_PTR(PTR_ERR(m->tagpool));
             }
     ...

     <--  snip  -->

Also spotted was a leak of the same structure further down in the function.

Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>