[PATCH] zd1211rw: Fix software encryption/decryption

Apparently the ZD1211 doesn't mind, but the ZD1211B absolutely must be
told that encryption is happening in software.

Signed-off-by: Daniel Drake <dsd@gentoo.org>
Signed-off-by: Ulrich Kunitz <kune@deine-taler.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>