smb: Initialize cfid->tcon before performing network ops

Avoid leaking a tcon ref when a lease break races with opening the
cached directory. Processing the leak break might take a reference to
the tcon in cached_dir_lease_break() and then fail to release the ref in
cached_dir_offload_close, since cfid->tcon is still NULL.

Fixes: ebe98f14 ("cifs: enable caching of directories for which a lease is held")
Signed-off-by: Paul Aurich <paul@darkrain42.org>
Signed-off-by: Steve French <stfrench@microsoft.com>