LINUX: dcache updates for mkdir and sillyrename

LINUX: dcache updates for mkdir and sillyrename

Commit d075b0549d62e4a81b7543b9c2f5dac242074909 introduced
parent_vcache_dv() to get the data version from fakestat mount points.
.mkdir (essentially .create for directories) should use this when
updating ->d_time.

In sillyrename, __dp is a negative dentry that should be forced to
revalidate since the new name in dentry now exists.

Change-Id: I5b112ce0437bfb061479024fee745b46821e599c
Reviewed-on: https://gerrit.openafs.org/12141
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>