package/openzwave: fix build with gcc 11

Set DEBUG_FLAGS and RELEASE_FLAGS to an empty value to remove -Werror
and fix the following build failure with gcc 11:

/tmp/instance-5/output-1/build/openzwave-62444b0f979c337d2091d77d89cf63c2ae9775cf/cpp/src/command_classes/AssociationCommandConfiguration.cpp: In member function 'virtual bool OpenZWave::Internal::CC::AssociationCommandConfiguration::HandleMsg(const uint8*, uint32, uint32)':
/tmp/instance-5/output-1/build/openzwave-62444b0f979c337d2091d77d89cf63c2ae9775cf/cpp/src/command_classes/AssociationCommandConfiguration.cpp:191:85: error: 'this' pointer is null [-Werror=nonnull]
  191 |                                                                 group->ClearCommands(nodeIdx);
      |                                                                 ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~

Fixes:
 - http://autobuild.buildroot.org/results/05ad5cc1f593704ef032f3c5278695247450b94b



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>