[PATCH] mac80211: fix printk warning on 64-bit

My AID message patch introduced a warning on 64-bit machines because ~
extends to unsigned long:

| net/mac80211/ieee80211_sta.c: In function ‘ieee80211_rx_mgmt_assoc_resp’:
| net/mac80211/ieee80211_sta.c:1187: warning: format ‘%d’ expects type ‘int’, but argument 7 has type ‘long unsigned int’

This fixes it by explicitly casting the result to u16 (which 'aid' is).

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