Silence -Wstringop-overflow warnings with gcc 14 on s390x

Silence -Wstringop-overflow warnings with gcc 14 on s390x

Compiling OpenSSL on s390x with gcc 14 (i.e. in Fedora 41) shows several
-Wstringop-overflow warnings in providers/implementations/rands/drbg_ctr.c
and test/params_api_test.c.

Add explicit length checks to let the compiler know that it won't overrun
the buffer. This also silences the warnings.

Signed-off-by: Ingo Franzki <ifranzki@linux.ibm.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/27710)