Fix build break on -release builds

Fix build break on -release builds

The OC_UNUSED macro is defined in octypes.h which is not included
by the source file. Switching to (void) to minimize the amount of
changes required to fix.

Change-Id: I76c13d448eb568b7f55dcd3974b8ee8891b01098
Signed-off-by: Mike Fenelon <mike.fenelon@microsoft.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/17757
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Alex Kelley <alexke@microsoft.com>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>