fs/9p: Workaround vfs rename rehash bug

This is similar to what ceph, ocfs2 and nfs does
http://kerneltrap.org/mailarchive/linux-fsdevel/2008/4/18/1498534



May be we should get vfs fixed

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>