zd1211rw: adding SONY IFU-WLM2 (054c:0257) as a zd1211b device

Yevgen Kotikov reported success on the sourceforge zd1211-devs list
with the following details:

Brand/retail: SONY IFU-WLM2
USB-IDs: Vendor: 0x054C Device: 0x0257
chip ID: zd1211b chip 054c:0257 v4802 high 00-0b-6b AL2230_RF pa0 -----
FCC ID: unknown

Signed-off-by: Hin-Tak Leung <htl10@users.sourceforge.net>
Tested-by: Yevgen Kotikov <yevgen.kotikov@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>