Bluetooth: btusb: mediatek: Fix double free of skb in coredump

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: btusb: mediatek: Fix double free of skb in coredump hci_devcd_append() would free the skb on error so the caller don't have to free it again otherwise it would cause the double free of skb. Reported-by : Dan Carpenter <dan.carpenter@linaro.org>