s_cb.c: Add missing return value checks

s_cb.c: Add missing return value checks

Return value of function 'SSL_CTX_ctrl', that is called from
SSL_CTX_set1_verify_cert_store() and SSL_CTX_set1_chain_cert_store(),
is not checked, but it is usually checked for this function.

CLA: trivial

Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23647)