can: rcar_can: fix IRQ check

rcar_can_probe() regards 0 as a wrong IRQ #, despite platform_get_irq() that it
calls returns negative error code in that case. This leads to the following
being printed to the console when attempting to open the device:

error requesting interrupt fffffffa

because  rcar_can_open() calls request_irq() with a negative IRQ #, and that
function naturally fails with -EINVAL.

Check for the negative error codes instead and propagate them upstream instead
of just returning -ENODEV.

Fixes: fd115931 ("can: add Renesas R-Car CAN driver")
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/rcar_can.c

@@ -758,8 +758,9 @@ static int rcar_can_probe(struct platform_device *pdev)
 	}
 
 	irq = platform_get_irq(pdev, 0);
-	if (!irq) {
+	if (irq < 0) {
 		dev_err(&pdev->dev, "No IRQ resource\n");
+		err = irq;
 		goto fail;
 	}