remove redundant zero assignments

The structure has already been initialized to zero with memset.
See also commit 64b25758

 (remove 0 assignments)

Signed-off-by: Cristian Stoica <cristian.stoica@nxp.com>
CLA: trivial
Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1463)