rsi: fix missing null pointer check from a failed ieee80211_probereq_get call

The call to ieee80211_probereq_get can return NULL if a skb allocation
fails, so add a null pointer check and free an earlier skb on the error
exit return path.

Fixes: 7fdcb8e1 ("rsi: add support for hardware scan offload")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/rsi/rsi_91x_mgmt.c

@@ -1726,6 +1726,10 @@ int rsi_send_bgscan_probe_req(struct rsi_common *common,
 
 	probereq_skb = ieee80211_probereq_get(common->priv->hw, vif->addr, ssid,
 					      ssid_len, scan_req->ie_len);
+	if (!probereq_skb) {
+		dev_kfree_skb(skb);
+		return -ENOMEM;
+	}
 
 	memcpy(&skb->data[frame_len], probereq_skb->data, probereq_skb->len);