eth: mlx4: Fix IS_ERR() vs NULL check bug in mlx4_en_create_rx_ring

[ Upstream commit e580bea ]

Replace NULL check with IS_ERR() check after calling page_pool_create()
since this function returns error pointers (ERR_PTR).
Using NULL check could lead to invalid pointer dereference.

Fixes: 8533b14 ("eth: mlx4: create a page pool for Rx")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Link: https://patch.msgid.link/20250828121858.67639-1-linmq006@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Yuuoniy

drivers/net/ethernet/mellanox/mlx4/en_rx.c

@@ -267,8 +267,10 @@ int mlx4_en_create_rx_ring(struct mlx4_en_priv *priv,
 	pp.dma_dir = priv->dma_dir;
 
 	ring->pp = page_pool_create(&pp);
-	if (!ring->pp)
+	if (IS_ERR(ring->pp)) {
+		err = PTR_ERR(ring->pp);
 		goto err_ring;
+	}
 
 	if (xdp_rxq_info_reg(&ring->xdp_rxq, priv->dev, queue_index, 0) < 0)
 		goto err_pp;