securebootcert build warnings

[Colin Ian King]

When building with scan-build I'm seeing this warning:

uefi/securebootcert/securebootcert.c:294:3: warning: Value stored to
'SignatureOwner' is never read
                SignatureOwner = *(EFI_GUID *)var_data_addr;
                ^                ~~~~~~~~~~~~~~~~~~~~~~~~~~

it seems that there is no validation occurring on SignatureOwner. Is
that intentional?  Can we fix this so we don't get this build warning?

Cheers,

Colin