Bluetooth: mgmt: Fix the command returns garbage parameter value

When the Get Device Flags command fails, it returns the error status
with the parameters filled with the garbage values. Although the
parameters are not used, it is better to fill with zero than the random
values.

Signed-off-by: Tedd Ho-Jeong An <tedd.an@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>