rtc: nct3018y: fix possible NULL dereference

alarm_enable and alarm_flag are allowed to be NULL but will be dereferenced
later by the dev_dbg call.

Reported-by: kernel test robot <[e-mail]>
Reported-by: Dan Carpenter <[e-mail]>
Closes: https://lore.kernel.org/r/[e-mail]/
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexandre Belloni <[e-mail]>

drivers/rtc/rtc-nct3018y.c

···
 		if (flags < 0)
 			return flags;
 		*alarm_enable = flags & NCT3018Y_BIT_AIE;
+		dev_dbg(&client->dev, "%s:alarm_enable:%x\n", __func__, *alarm_enable);
+
 	}
 
 	if (alarm_flag) {
···
 		if (flags < 0)
 			return flags;
 		*alarm_flag = flags & NCT3018Y_BIT_AF;
+		dev_dbg(&client->dev, "%s:alarm_flag:%x\n", __func__, *alarm_flag);
 	}
-
-	dev_dbg(&client->dev, "%s:alarm_enable:%x alarm_flag:%x\n",
-		__func__, *alarm_enable, *alarm_flag);
 
 	return 0;
 }