Bluetooth: Enable -D__CHECK_ENDIAN__ for sparse by default

The Bluetooth protocol and hardware is pretty much all little endian
and so when running sparse via "make C=2" for example, enable the
endian checks by default.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>