power: reset: xgene-reboot: Fix a NULL vs IS_ERR() test

The devm_platform_ioremap_resource() function returns error points. It
never returns NULL. Update the check accordingly.

Fixes: 7ddfd33c6ee5 ("power: reset: xgene-reboot: Use devm_platform_ioremap_resource() helper")
Signed-off-by: Dan Carpenter <[e-mail]>
Acked-by: Andrew Davis <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Sebastian Reichel <[e-mail]>

drivers/power/reset/xgene-reboot.c

···
 		return -ENOMEM;
 
 	ctx->csr = devm_platform_ioremap_resource(pdev, 0);
-	if (!ctx->csr) {
+	if (IS_ERR(ctx->csr)) {
 		dev_err(dev, "can not map resource\n");
-		return -ENODEV;
+		return PTR_ERR(ctx->csr);
 	}
 
 	if (of_property_read_u32(dev->of_node, "mask", &ctx->mask))