[PATCH] zd1211rw: 16-bit writes for physical control registers

Caused by the fact that physical control registers appear to have
only a width of 16 bit, 32-bit writes are not required.

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