Fix type of ptr field.
Fix type of ptr field.

Since "ptr" is used to handle arbitrary other types it should be
void *.

Reviewed-by: Rich Salz <c04971a99e5a9ee80eaab4b1deb37e845b0bd697@openssl.org>

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl