sata_fsl: fix error handling of irq_of_parse_and_map

irq_of_parse_and_map() returns 0 on error (the result is unsigned int),
so testing for negative result never works.

Signed-off-by: Dmitry Torokhov <dtor@chromium.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org
diff --git a/drivers/ata/sata_fsl.c b/drivers/ata/sata_fsl.c
index 07bc7e4..6507159 100644
--- a/drivers/ata/sata_fsl.c
+++ b/drivers/ata/sata_fsl.c
@@ -1488,7 +1488,7 @@
 	host_priv->csr_base = csr_base;
 
 	irq = irq_of_parse_and_map(ofdev->dev.of_node, 0);
-	if (irq < 0) {
+	if (!irq) {
 		dev_err(&ofdev->dev, "invalid irq from platform\n");
 		goto error_exit_with_cleanup;
 	}