fs/9p: re-init the wstat in readdir loop

This ensure that on failure when we free the stat buf we don't end up
freeing an already freed pointer in the earlier loop

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Sripathi Kodi <sripathik@in.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>