Convert ossl_ocsp.c to opaque ASN1_STRING

OpenSSL plans to make asn1_string_st opaque, the struct underlying most
ASN.1 types such as ASN1_*STRING, ASN1_ENUMERATED, ASN1_INTEGER, etc. 
Most of ruby/openssl's C code can be straigtforwardly converted to use
accessors available since OpenSS

Author: botovq

ext/openssl/ossl_ocsp.c

@@ -1550,8 +1550,9 @@ ossl_ocspcid_get_issuer_name_hash(VALUE self)
     GetOCSPCertId(self, id);
     OCSP_id_get0_info(&name_hash, NULL, NULL, NULL, id);
 
-    ret = rb_str_new(NULL, name_hash->length * 2);
-    ossl_bin2hex(name_hash->data, RSTRING_PTR(ret), name_hash->length);
+    ret = rb_str_new(NULL, ASN1_STRING_length(name_hash) * 2);
+    ossl_bin2hex(ASN1_STRING_get0_data(name_hash), RSTRING_PTR(ret),
+                 ASN1_STRING_length(name_hash));
 
     return ret;
 }
@@ -1573,8 +1574,9 @@ ossl_ocspcid_get_issuer_key_hash(VALUE self)
     GetOCSPCertId(self, id);
     OCSP_id_get0_info(NULL, NULL, &key_hash, NULL, id);
 
-    ret = rb_str_new(NULL, key_hash->length * 2);
-    ossl_bin2hex(key_hash->data, RSTRING_PTR(ret), key_hash->length);
+    ret = rb_str_new(NULL, ASN1_STRING_length(key_hash) * 2);
+    ossl_bin2hex(ASN1_STRING_get0_data(key_hash), RSTRING_PTR(ret),
+                 ASN1_STRING_length(key_hash));
 
     return ret;
 }