Windows: change buf_Find*() signature to accept cm_fid_t

Windows: change buf_Find*() signature to accept cm_fid_t

The buf_Find*() functions require a cm_fid_t to match with the
cm_buf_t objects not a cm_scache_t.  Change the signature so
that the cm_scache_t is not required.  It should be possible to
search for a buffer even if the cm_scache_t is not present in
the cache.

Change-Id: I38835ee86405c4f3f798ad6be8626e6da507109f
Reviewed-on: http://gerrit.openafs.org/5304
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>