net: stmmac: Check return value of alloc_dma_desc_resources()

alloc_dma_desc_resources() returns an error value and the next line
actually checks for it, so assign the return value properly.

Found by the coverity scanner.
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Acked-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -1705,7 +1705,7 @@ static int stmmac_open(struct net_device *dev)
 	priv->dma_rx_size = STMMAC_ALIGN(dma_rxsize);
 	priv->dma_buf_sz = STMMAC_ALIGN(buf_sz);
 
-	alloc_dma_desc_resources(priv);
+	ret = alloc_dma_desc_resources(priv);
 	if (ret < 0) {
 		pr_err("%s: DMA descriptors allocation failed\n", __func__);
 		goto dma_desc_error;