examples/security: fix 'private' key mention to 'public' to avoid confusion
examples/security: fix 'private' key mention to 'public' to avoid confusion

Change-Id: I784993107ae11979302e543997ed61877679b6f1
Signed-off-by: Gregory Lemercier <8dfc97fc6edd815cc4739eb8e7c74f3c8222d00f@samsung.com>

JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT