irqchip/irq-mvebu-sei: Fix a NULL vs IS_ERR() bug in probe function

The devm_ioremap_resource() function never returns NULL, it returns
error pointers.

Fixes: 61ce8d8d8a81 ("irqchip/irq-mvebu-sei: Add new driver for Marvell SEI")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Gregory Clement <gregory.clement@bootlin.com>
Cc: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: kernel-janitors@vger.kernel.org
Link: https://lkml.kernel.org/r/20181013102246.GD16086@mwanda

drivers/irqchip/irq-mvebu-sei.c

@@ -384,9 +384,9 @@ static int mvebu_sei_probe(struct platform_device *pdev)
 
 	sei->res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	sei->base = devm_ioremap_resource(sei->dev, sei->res);
-	if (!sei->base) {
+	if (IS_ERR(sei->base)) {
 		dev_err(sei->dev, "Failed to remap SEI resource\n");
-		return -ENODEV;
+		return PTR_ERR(sei->base);
 	}
 
 	/* Retrieve the SEI capabilities with the interrupt ranges */