net: stmicro: fix a missing check of clk_prepare

clk_prepare() could fail, so let's check its status, and if it fails,
return its error code upstream.
Signed-off-by: Kangjie Lu <kjlu@umn.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/dwmac-sunxi.c

@@ -59,7 +59,9 @@ static int sun7i_gmac_init(struct platform_device *pdev, void *priv)
 		gmac->clk_enabled = 1;
 	} else {
 		clk_set_rate(gmac->tx_clk, SUN7I_GMAC_MII_RATE);
-		clk_prepare(gmac->tx_clk);
+		ret = clk_prepare(gmac->tx_clk);
+		if (ret)
+			return ret;
 	}
 
 	return 0;