wil6210: fix potential null dereference of ndev before null check

The pointer ndev is being dereferenced before it is being null checked,
hence there is a potential null pointer deference. Fix this by only
dereferencing ndev after it has been null checked

Detected by CoverityScan, CID#1467010 ("Dereference before null check")

Fixes: e00243fa ("wil6210: infrastructure for multiple virtual interfaces")
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Reviewed-by: NMaya Erez <merez@codeaurora.org>
Signed-off-by: NKalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/ath/wil6210/main.c

@@ -391,7 +391,7 @@ static void wil_fw_error_worker(struct work_struct *work)
 	struct wil6210_priv *wil = container_of(work, struct wil6210_priv,
 						fw_error_worker);
 	struct net_device *ndev = wil->main_ndev;
-	struct wireless_dev *wdev = ndev->ieee80211_ptr;
+	struct wireless_dev *wdev;
 
 	wil_dbg_misc(wil, "fw error worker\n");
 
@@ -399,6 +399,7 @@ static void wil_fw_error_worker(struct work_struct *work)
 		wil_info(wil, "No recovery - interface is down\n");
 		return;
 	}
+	wdev = ndev->ieee80211_ptr;
 
 	/* increment @recovery_count if less then WIL6210_FW_RECOVERY_TO
 	 * passed since last recovery attempt