Windows: buf_GetNewLocked should use cleaned cm_buf

Windows: buf_GetNewLocked should use cleaned cm_buf

buf_GetNewLocked() searches the free buffer list for a buffer
that has a 0 refcnt, is not in the chunk that is being populated,
is not actively having I/O performed on it and is not dirty.
If it comes across a dirty buffer, it calls buf_Clean() with
the assumption that buf_CleanAsync() (as it was previously called)
was in fact asynchronous and would return immediately.  Instead
buf_Clean() is synchronous and when it completes the buffer will
in most cases be clean.  buf_GetNewLocked() should use the newly
cleaned buffer if it is still available and not continue the
search from the next entry in the free buffer list.

Change-Id: Iae629df57b9d27a813f7f4c6740be23bd33fe039
Reviewed-on: http://gerrit.openafs.org/6174
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>