libfec: return raw and corrected verity metadata signatures

Since it's not possible for libfec to identify whether the signature
field was successfully corrected, return both and allow the caller to
validate either signature.

Bug: 28943429
Change-Id: Ie913c21ba1d07d6df4c6feeb7226b2ec963f4d19
(cherry picked from commit 65cbaeb020b209f3d75d594ebbe49a609dd3c7e7)
4 files changed