ipw2200 fix: ->rt_chbitmask is le16

A couple of places forgot cpu_to_le16() in assignments to
that field, even though right next to those in other branches
of if-else we do it correctly.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: John W. Linville <linville@tuxdriver.com>