LINUX: afs_create infinite fetchStatus loop

LINUX: afs_create infinite fetchStatus loop

For a file in a directory with the CStatd bit cleared, we can get
an infinite fetchStatus loop.

In afs_create(), afs_getDCache() may return NULL due to an error.
If unchecked it will loop which may produce multiple fetchStatus()
calls to the fileserver.

Credit: Yadav Yadavendra for identifying and analysing this issue.

Change-Id: Iecd77d49a5f3e8bb629396c57246736b39aa935f
Reviewed-on: https://gerrit.openafs.org/12651
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>