9pfs: fix potential segfault during walk

9pfs: fix potential segfault during walk

If the call to fid_to_qid() returns an error, we will call v9fs_path_free()
on uninitialized paths.

It is a regression introduced by the following commit:

56f101ecce0e 9pfs: handle walk of ".." in the root directory

Let's fix this by initializing dpath and path before calling fid_to_qid().

Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
[groug: updated the changelog to indicate this is regression and to provide
        the offending commit SHA1]
Signed-off-by: Greg Kurz <groug@kaod.org>
(cherry picked from commit 13fd08e631ec0c3ff5ad1bdcb6a4474c7d9a024f)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>