Update templating inside cholesky_decompose

Author: WardBrian

stan/math/prim/fun/cholesky_decompose.hpp

@@ -1,11 +1,9 @@
 #ifndef STAN_MATH_PRIM_FUN_CHOLESKY_DECOMPOSE_HPP
 #define STAN_MATH_PRIM_FUN_CHOLESKY_DECOMPOSE_HPP
 
+#include <stan/math/prim/fun/Eigen.hpp>
 #include <stan/math/prim/meta.hpp>
 #include <stan/math/prim/err.hpp>
-#include <stan/math/prim/fun/Eigen.hpp>
-
-#include <cmath>
 
 namespace stan {
 namespace math {
@@ -31,12 +29,11 @@ template <typename EigMat, require_eigen_t<EigMat>* = nullptr,
 inline Eigen::Matrix<value_type_t<EigMat>, EigMat::RowsAtCompileTime,
                      EigMat::ColsAtCompileTime>
 cholesky_decompose(const EigMat& m) {
-  const eval_return_type_t<EigMat>& m_eval = m.eval();
+  using PlainMat = plain_type_t<EigMat>;
+  PlainMat m_eval = m;
   check_symmetric("cholesky_decompose", "m", m_eval);
   check_not_nan("cholesky_decompose", "m", m_eval);
-  Eigen::LLT<Eigen::Matrix<value_type_t<EigMat>, EigMat::RowsAtCompileTime,
-                           EigMat::ColsAtCompileTime>>
-      llt = m_eval.llt();
+  Eigen::LLT<PlainMat> llt = m_eval.llt();
   check_pos_definite("cholesky_decompose", "m", llt);
   return llt.matrixL();
 }