Fix aix compile error in cmp_ctx_test.c

Fix aix compile error in cmp_ctx_test.c

Errors were of the form 1506-226 (S) The ":" operator is not allowed between "int" and "char*".
I think it is valid syntax the way it was written, But just rewrote so it compiled.
The aix compiler must be looking at the type of blah() when doing test ? (blah(), NULL) : X.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11698)