Fix build with TinyCBOR from the dev branch: stop using internal API

Fix build with TinyCBOR from the dev branch: stop using internal API

Using the CborEncoder "ptr" member is deprecated. TinyCBOR 0.3
introduced two functions that replace the uses we had here. TinyCBOR 0.4
will rename those members.

Change-Id: I0031aa609e714ae983c3fffd14664c21b9460423
Signed-off-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/9867
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Uze Choi <uzchoi@samsung.com>
Reviewed-by: David Antler <david.a.antler@intel.com>
Reviewed-by: Dave Thaler <dthaler@microsoft.com>
Reviewed-by: Habib Virji <habib.virji@samsung.com>