Bluetooth: btusb: Fix memory leak in btusb_mtk_wmt_recv

In btusb_mtk_wmt_recv if skb_clone fails, the alocated skb should be
released.

Omit the labels “err_out” and “err_free_skb” in this function
implementation so that the desired exception handling code
would be directly specified in the affected if branches.

Fixes: a1c49c43

 ("btusb: Add protocol support for MediaTek MT7668U USB devices")
Signed-off-by: Jupeng Zhong <zhongjupeng@yulong.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>