Build currently fails with -Werror=maybe-uninitialized set:
net/wireless/nl80211.c: In function '__cfg80211_wdev_from_attrs':
net/wireless/nl80211.c:124:44: error: 'wdev_id' may be used
uninitialized in this function [-Werror=maybe-uninitialized]
Easy fix is to just initialize wdev_id to 0, since it's value doesn't
otherwise matter unless have_wdev_id is true.