rtc: sysfs: fix NULL check in rtc_add_groups()

mainline inclusion
from mainline-4.20-rc1
commit 777d8ae5
category: bugfix
bugzilla: 6616
CVE: NA

-------------------------------------------------

devm_kcalloc() returns NULL, it never returns error pointers.  In the
current code we would return PTR_ERR(NULL) which is success, instead of
returning the -ENOMEM error code.

Fixes: a0a1a1ba ("rtc: sysfs: facilitate attribute add to rtc device")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NAlexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: NZhang Dianfang <zhangdianfang@huawei.com>
Reviewed-by: NHanjun Guo <guohanjun@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/rtc/rtc-sysfs.c

@@ -338,8 +338,8 @@ int rtc_add_groups(struct rtc_device *rtc, const struct attribute_group **grps)
 
 	new_cnt = old_cnt + add_cnt + 1;
 	groups = devm_kcalloc(&rtc->dev, new_cnt, sizeof(*groups), GFP_KERNEL);
-	if (IS_ERR_OR_NULL(groups))
-		return PTR_ERR(groups);
+	if (!groups)
+		return -ENOMEM;
 	memcpy(groups, rtc->dev.groups, old_cnt * sizeof(*groups));
 	memcpy(groups + old_cnt, grps, add_cnt * sizeof(*groups));
 	groups[old_cnt + add_cnt] = NULL;