rtc: gamecube: Fix an IS_ERR() vs NULL check

The devm_kzalloc() function returns NULL on error, it doesn't return
error pointers.

Fixes: 86559400b3 ("rtc: gamecube: Add a RTC driver for the GameCube, Wii and Wii U")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220107073340.GF22086@kili

drivers/rtc/rtc-gamecube.c

@@ -319,8 +319,8 @@ static int gamecube_rtc_probe(struct platform_device *pdev)
 	int ret;
 
 	d = devm_kzalloc(dev, sizeof(struct priv), GFP_KERNEL);
-	if (IS_ERR(d))
-		return PTR_ERR(d);
+	if (!d)
+		return -ENOMEM;
 
 	d->iob = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(d->iob))