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: a05829a ("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>

net/wireless/nl80211.c

@@ -70,7 +70,7 @@ __cfg80211_wdev_from_attrs(struct cfg80211_registered_device *rdev,
 	struct wireless_dev *result = NULL;
 	bool have_ifidx = attrs[NL80211_ATTR_IFINDEX];
 	bool have_wdev_id = attrs[NL80211_ATTR_WDEV];
-	u64 wdev_id;
+	u64 wdev_id = 0;
 	int wiphy_idx = -1;
 	int ifidx = -1;