cifs: make cnvrtDosUnixTm take a little-endian args and an offset

The callers primarily end up converting the args from le anyway. Also,
most of the callers end up needing to add an offset to the result. The
exception to these rules is cnvrtDosCifsTm, but there are no callers of
that function, so we might as well remove it.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Steve French <sfrench@us.ibm.com>