9p: don't leave a half-initialized inode sitting around

[ Upstream commit 0a73d0a204a4a04a1e110539c5a524ae51f91d6d ]

Cc: stable@vger.kernel.org # all branches
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>