wireless/nl80211: fix wdev_id may be used uninitialized

wireless/nl80211: fix wdev_id may be used uninitialized

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.

Fixes: a05829a7222e ("cfg80211: avoid holding the RTNL when calling the driver")
CC: Johannes Berg <johannes@sipsolutions.net>
CC: "David S. Miller" <davem@davemloft.net>
CC: Jakub Kicinski <kuba@kernel.org>
CC: linux-wireless@vger.kernel.org
CC: netdev@vger.kernel.org
Signed-off-by: Jarod Wilson <jarod@redhat.com>
Link: https://lore.kernel.org/r/20210312163651.1398207-1-jarod@redhat.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>