stmmac: do not fail when probe and there is no csr clk defined

On some platforms, for example where we are doing the bring-up,
the csr clock is not passed from the framework and the Ethernet
device driver is failing when it can work w/o any issues and
using the default values. So this patch just warnings the case
of the csr clock cannot be acquired but w/o failing the probe
step. I have just tested it on ST STiH415 SoC (ARM).

Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index efc42e1..1a4cf81 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -168,6 +168,9 @@
 #ifdef CONFIG_HAVE_CLK
 	u32 clk_rate;
 
+	if (IS_ERR(priv->stmmac_clk))
+		return;
+
 	clk_rate = clk_get_rate(priv->stmmac_clk);
 
 	/* Platform provided default clk_csr would be assumed valid
@@ -1923,7 +1926,7 @@
 	}
 
 	if (stmmac_clk_get(priv))
-		goto error;
+		pr_warning("%s: warning: cannot get CSR clock\n", __func__);
 
 	/* If a specific clk_csr value is passed from the platform
 	 * this means that the CSR Clock Range selection cannot be