[PATCH] cfg80211: fix signed macaddress in sysfs

Fix signedness mixup making mac addresses show up strangely
(like 00:11:22:33:44:ffffffaa) in /sys/class/ieee80211/*/macaddress.

Signed-off-by: David Lamparter <equinox@diac24.net>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>