mt76: mt7615: Fix memory leak in mt7615_mcu_wtbl_sta_add()

In the Linux kernel, the following vulnerability has been resolved: mt76: mt7615: Fix memory leak in mt7615_mcu_wtbl_sta_add() In mt7615_mcu_wtbl_sta_add(), an skb sskb is allocated. If the subsequent call to mt76_connac_mcu_alloc_wtbl_req() fails, the function returns an error without freeing sskb, leading to a memory leak. Fix this by calling dev_kfree_skb() on sskb in the error handling path to ensure it is properly released.