spi-imx: correct check for platform_get_irq failing

platform_get_irq returns -ENXIO if there is no entry.  So ensure
return value is greater than zero instead of non-zero.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/spi/spi_imx.c

@@ -555,7 +555,7 @@ static int __init spi_imx_probe(struct platform_device *pdev)
 	}
 
 	spi_imx->irq = platform_get_irq(pdev, 0);
-	if (!spi_imx->irq) {
+	if (spi_imx->irq <= 0) {
 		ret = -EINVAL;
 		goto out_iounmap;
 	}