spi: tegra: don't treat NULL clk as an error

Some platforms have been known to return NULL from clk_get() if they
support only a single struct clk.  Whilst tegra doesn't do this, make
the drivers consistent with others.
Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Acked-by: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/spi/spi_tegra.c

@@ -513,7 +513,7 @@ static int __init spi_tegra_probe(struct platform_device *pdev)
 	}
 
 	tspi->clk = clk_get(&pdev->dev, NULL);
-	if (IS_ERR_OR_NULL(tspi->clk)) {
+	if (IS_ERR(tspi->clk)) {
 		dev_err(&pdev->dev, "can not get clock\n");
 		ret = PTR_ERR(tspi->clk);
 		goto err2;