openssl-cmp.pod.in: replace the term 'verify' by the more correct 'validate'
openssl-cmp.pod.in: replace the term 'verify' by the more correct 'validate'

Reviewed-by: Tomas Mraz <2bc6038c3dfca09b2da23c8b6da8ba884dc2dcc2@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14018)

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