In contrib/opie/opiekey.c, use the correct length to zero the secret.
In contrib/opie/opiekey.c, use the correct length to zero the secret.

Found by:	clang ToT
Reviewed by:	delphij
MFC after:	3 days

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase