Use kfree_skb() instead of kfree() to free sk_buff.

Fixes: 2faa3f15 ("Bluetooth: hci_qca: wcn3990: Drop baudrate change vendor event")
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: NMatthias Kaehlcke <mka@chromium.org>
Signed-off-by: NMarcel Holtmann <marcel@holtmann.org>