Bluetooth: Get rid of cmd_timeout and use the reset callback

The hdev->reset is never used now and the hdev->cmd_timeout actually
does reset. This patch changes the call path from
  hdev->cmd_timeout -> vendor_cmd_timeout -> btusb_reset -> hdev->reset
, to
  hdev->reset -> vendor_reset -> btusb_reset
Which makes it clear when we export the hdev->reset to a wider usage
e.g. allowing reset from sysfs.

This patch doesn't introduce any behavior change.

Signed-off-by: Hsin-chen Chuang <chharry@chromium.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>