diffie-hellman: Use bool instead of status_t as get_shared_secret() return value

While such a change is not unproblematic, keeping status_t makes the API
inconsistent once we introduce return values for the public value operations.

src/libcharon/plugins/ha/ha_dispatcher.c

@@ -81,11 +81,11 @@ struct ha_diffie_hellman_t {
 	chunk_t pub;
 };
 
-METHOD(diffie_hellman_t, dh_get_shared_secret, status_t,
+METHOD(diffie_hellman_t, dh_get_shared_secret, bool,
 	ha_diffie_hellman_t *this, chunk_t *secret)
 {
 	*secret = chunk_clone(this->secret);
-	return SUCCESS;
+	return TRUE;
 }
 
 METHOD(diffie_hellman_t, dh_get_my_public_value, void,