rtc: rc5t619: Fix an ERR_PTR vs NULL check

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

Fixes: 540d1e15 ("rtc: rc5t619: Add Ricoh RC5T619 RTC driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20200407092852.GI68494@mwandaSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-rc5t619.c

@@ -356,10 +356,8 @@ static int rc5t619_rtc_probe(struct platform_device *pdev)
 	int err;
 
 	rtc = devm_kzalloc(dev, sizeof(*rtc), GFP_KERNEL);
-	if (IS_ERR(rtc)) {
-		err = PTR_ERR(rtc);
+	if (!rtc)
 		return -ENOMEM;
-	}
 
 	rtc->rn5t618 = rn5t618;