rtc: mt6397: check return value after calling platform_get_resource()

It will cause null-ptr-deref if platform_get_resource() returns NULL,
we need check the return value.

Fixes: fc297911 ("rtc: mediatek: Add MT6397 RTC driver")
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Reviewed-by: NAngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: NAlexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220505125043.1594771-1-yangyingliang@huawei.com

drivers/rtc/rtc-mt6397.c

@@ -269,6 +269,8 @@ static int mtk_rtc_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!res)
+		return -EINVAL;
 	rtc->addr_base = res->start;
 
 	rtc->data = of_device_get_match_data(&pdev->dev);