Fix opencl

Author: andrjohns

stan/math/prim/prob/std_normal_lpdf.hpp

@@ -43,7 +43,7 @@ return_type_t<T_y> std_normal_lpdf(const T_y& y) {
     return 0.0;
   }
 
-  T_partials_return y_val = as_value_column_vector_or_scalar(y_ref);
+  const auto& y_val = as_value_column_vector_or_scalar(y_ref);
   T_partials_return logp = -dot_self(y_val) / 2.0;
   auto ops_partials = make_partials_propagator(y_ref);
 

test/unit/math/mix/prob/std_normal_test.cpp

@@ -7,4 +7,12 @@ TEST_F(AgradRev, mathMixScalFun_std_normal) {
   stan::test::expect_ad(f, -0.3);
   stan::test::expect_ad(f, 0.0);
   stan::test::expect_ad(f, 1.7);
+
+  Eigen::VectorXd x(3);
+  x << -0.3, 0.0, 1.7;
+  std::vector<double> x2{0.0, 1.7};
+
+  stan::test::expect_ad(f, x);
+  stan::test::expect_ad(f, x.transpose().eval());
+  stan::test::expect_ad(f, x2);
 }