DPE: Fix CertifyKey when layer is finalized

When layer is finalized the CertifyKey should open
a new layer.

Change-Id: I7c86d77bf12603472435bb93abd6ef6d42ddccef
Signed-off-by: Tamas Ban <tamas.ban@arm.com>
Signed-off-by: Maulik Patel <maulik.patel@arm.com>
3 files changed