Bluetooth: btusb: disable by default Qualcomm multi-subsystem

New knobs should default to 'n'. The mentioned one depends on
BT_HCIBTUSB, but the latter is enabled on most systems.

Acked-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>