net: macb: fix build warning

We are getting build warning about:
macb.c:2889:13: warning: 'tx_clk' may be used uninitialized in this function
macb.c:2888:11: warning: 'hclk' may be used uninitialized in this function

In reality they are not used uninitialized as clk_init() will initialize
them, this patch will just silence the warning.
Signed-off-by: NSudip Mukherjee <sudip@vectorindia.org>
Acked-by: NNicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/cadence/macb.c

@@ -2823,7 +2823,7 @@ static int macb_probe(struct platform_device *pdev)
 	struct device_node *np = pdev->dev.of_node;
 	struct device_node *phy_node;
 	const struct macb_config *macb_config = NULL;
-	struct clk *pclk, *hclk, *tx_clk;
+	struct clk *pclk, *hclk = NULL, *tx_clk = NULL;
 	unsigned int queue_mask, num_queues;
 	struct macb_platform_data *pdata;
 	bool native_io;