Fix memory leak in cmp_calc_protection()

Triggered by a  memory allocation failure.
Detected by PR #18355

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: David von Oheimb <david.von.oheimb@siemens.com>
(Merged from https://github.com/openssl/openssl/pull/18670)

crypto/cmp/cmp_protect.c

@@ -91,7 +91,7 @@ ASN1_BIT_STRING *ossl_cmp_calc_protection(const OSSL_CMP_CTX *ctx,
             goto end;
 
         if ((prot = ASN1_BIT_STRING_new()) == NULL)
-            return NULL;
+            goto end;
         /* OpenSSL defaults all bit strings to be encoded as ASN.1 NamedBitList */
         prot->flags &= ~(ASN1_STRING_FLAG_BITS_LEFT | 0x07);
         prot->flags |= ASN1_STRING_FLAG_BITS_LEFT;