crypto/cmp/cmp_genm.c: avoid strcat() in get_genm_itav()

crypto/cmp/cmp_genm.c: avoid strcat() in get_genm_itav()

There is no need to use strcat() there, as it concatenates into a string
that is used in a format string anyway.  Put the literal prefix
into the format string and avoid literal string copying.

Fixes: d477484d33b7 "CMP: add support for genm/genp messages with id-it-caCerts"
Signed-off-by: Eugene Syromiatnikov <esyr@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.foundation>
Reviewed-by: Nikola Pajkovsky <nikolap@openssl.org>
Reviewed-by: Bob Beck <beck@openssl.org>
Reviewed-by: David von Oheimb <david.von.oheimb@siemens.com>
MergeDate: Tue May 26 14:54:19 2026
(Merged from https://github.com/openssl/openssl/pull/31230)