drivers: net: xgene: Check for IS_ERR rather than NULL for clock.

This patches fixes the code to check for IS_ERR rather
than NULL for clock interface.

Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Signed-off-by: Suman Tripathi <stripathi@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/apm/xgene/xgene_enet_xgmac.c b/drivers/net/ethernet/apm/xgene/xgene_enet_xgmac.c
index 27ba2fe..05edb84 100644
--- a/drivers/net/ethernet/apm/xgene/xgene_enet_xgmac.c
+++ b/drivers/net/ethernet/apm/xgene/xgene_enet_xgmac.c
@@ -256,9 +256,11 @@
 	if (!xgene_ring_mgr_init(pdata))
 		return -ENODEV;
 
-	clk_prepare_enable(pdata->clk);
-	clk_disable_unprepare(pdata->clk);
-	clk_prepare_enable(pdata->clk);
+	if (!IS_ERR(pdata->clk)) {
+		clk_prepare_enable(pdata->clk);
+		clk_disable_unprepare(pdata->clk);
+		clk_prepare_enable(pdata->clk);
+	}
 
 	xgene_enet_ecc_init(pdata);
 	xgene_enet_config_ring_if_assoc(pdata);
@@ -285,7 +287,8 @@
 
 static void xgene_enet_shutdown(struct xgene_enet_pdata *pdata)
 {
-	clk_disable_unprepare(pdata->clk);
+	if (!IS_ERR(pdata->clk))
+		clk_disable_unprepare(pdata->clk);
 }
 
 static void xgene_enet_link_state(struct work_struct *work)