Bluetooth: btusb: Fix incorrect type in assignment and uninitialized symbol

Warnings: drivers/bluetooth/btusb.c:3775 btusb_mtk_setup() error:
uninitialized symbol 'fw_version'.
-> add initial value for fw_version.

Warnings: sparse: sparse: incorrect type in assignment (different base
types)
-> add le32_to_cpu to fix incorrect type in assignment.

Signed-off-by: mark-yw.chen <mark-yw.chen@mediatek.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>