TESTS: Fix build warning for test-ovdk-stats.c

Change-Id: I1a281d08ba02a7ae4fd4e919e1890ca93e62afcd
Signed-off-by: Rory Sexton <rory.sexton@intel.com>
Reviewed-by: Meghan Halton <meghan.halton@intel.com>
Acked-by: Mark Kavanagh <mark.b.kavanagh@intel.com>