Fix a memory leak in cxsparse.cc

Thanks to Alexander Mordvintsev for reporting it.

Change-Id: Ia872be42ce80209e46722fc16a928496cf97e256
diff --git a/internal/ceres/cxsparse.cc b/internal/ceres/cxsparse.cc
index 21c98e0..19fa17c 100644
--- a/internal/ceres/cxsparse.cc
+++ b/internal/ceres/cxsparse.cc
@@ -116,12 +116,12 @@
   return cs_compress(&tsm_wrapper);
 }
 
-void CXSparse::Free(cs_di* factor) {
-  cs_free(factor);
+void CXSparse::Free(cs_di* sparse_matrix) {
+  cs_di_spfree(sparse_matrix);
 }
 
-void CXSparse::Free(cs_dis* factor) {
-  cs_sfree(factor);
+void CXSparse::Free(cs_dis* symbolic_factorization) {
+  cs_di_sfree(symbolic_factorization);
 }
 
 }  // namespace internal