[bug report] mt76: implement functions to get the response skb for MCU calls

[Dan Carpenter]

Hello Felix Fietkau,

The patch ae5ad6272d25: "mt76: implement functions to get the
response skb for MCU calls" from Sep 30, 2020, leads to the following
Smatch static checker warning:

	drivers/net/wireless/mediatek/mt76/mt7921/mcu.c:1151 mt7921_mcu_get_eeprom()
	error: potentially dereferencing uninitialized 'skb'.

drivers/net/wireless/mediatek/mt76/mt7921/mcu.c
    1136 int mt7921_mcu_get_eeprom(struct mt7921_dev *dev, u32 offset)
    1137 {
    1138         struct mt7921_mcu_eeprom_info req = {
    1139                 .addr = cpu_to_le32(round_down(offset, 16)),
    1140         };
    1141         struct mt7921_mcu_eeprom_info *res;
    1142         struct sk_buff *skb;
    1143         int ret;
    1144         u8 *buf;
    1145 
    1146         ret = mt76_mcu_send_and_get_msg(&dev->mt76, MCU_EXT_CMD_EFUSE_ACCESS, &req,
    1147                                         sizeof(req), true, &skb);

If mt76_mcu_send_and_get_msg() calls the dev->mcu_ops->mcu_send_msg()
then "skb" is not initialized.

    1148         if (ret)
    1149                 return ret;
    1150 
--> 1151         res = (struct mt7921_mcu_eeprom_info *)skb->data;
    1152         buf = dev->mt76.eeprom.data + le32_to_cpu(res->addr);
    1153         memcpy(buf, res->data, 16);
    1154         dev_kfree_skb(skb);
    1155 
    1156         return 0;
    1157 }

regards,
dan carpenter