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>
diff --git a/drivers/spi/spi_imx.c b/drivers/spi/spi_imx.c
index 8ffa48c..c96804f 100644
--- a/drivers/spi/spi_imx.c
+++ b/drivers/spi/spi_imx.c
@@ -555,7 +555,7 @@
 	}
 
 	spi_imx->irq = platform_get_irq(pdev, 0);
-	if (!spi_imx->irq) {
+	if (spi_imx->irq <= 0) {
 		ret = -EINVAL;
 		goto out_iounmap;
 	}