net: stmmac: fix csr_clk can't be zero issue

The specific clk_csr value can be zero, and
stmmac_clk is necessary for MDC clock which can be set dynamically.
So, change the condition from plat->clk_csr to plat->stmmac_clk to
fix clk_csr can't be zero issue.

Fixes: cd7201f4 ("stmmac: MDC clock dynamically based on the csr clock input")
Signed-off-by: Biao Huang <biao.huang@mediatek.com>
Acked-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -4380,10 +4380,10 @@ int stmmac_dvr_probe(struct device *device,
 	 * set the MDC clock dynamically according to the csr actual
 	 * clock input.
 	 */
-	if (!priv->plat->clk_csr)
-		stmmac_clk_csr_set(priv);
-	else
+	if (priv->plat->clk_csr >= 0)
 		priv->clk_csr = priv->plat->clk_csr;
+	else
+		stmmac_clk_csr_set(priv);
 
 	stmmac_check_pcs_mode(priv);
 

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

@@ -408,7 +408,10 @@ stmmac_probe_config_dt(struct platform_device *pdev, const char **mac)
 	/* Default to phy auto-detection */
 	plat->phy_addr = -1;
 
-	/* Get clk_csr from device tree */
+	/* Default to get clk_csr from stmmac_clk_crs_set(),
+	 * or get clk_csr from device tree.
+	 */
+	plat->clk_csr = -1;
 	of_property_read_u32(np, "clk_csr", &plat->clk_csr);
 
 	/* "snps,phy-addr" is not a standard property. Mark it as deprecated