crypto: ccp - memset structure fields to zero before reuse

The AES GCM function reuses an 'op' data structure, which members
contain values that must be cleared for each (re)use.

This fix resolves a crypto self-test failure:
alg: aead: gcm-aes-ccp encryption test failed (wrong result) on test vector 2, cfg="two even aligned splits"

Fixes: 36cf515b ("crypto: ccp - Enable support for AES GCM on v5 CCPs")
Cc: <stable@vger.kernel.org>
Signed-off-by: Gary R Hook <gary.hook@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>