Fix error reporting for missing axis (#2835)

* Fix error reporting for missing axis

* Update data_layout.cc

src/lang/data_layout.cc

@@ -5,6 +5,7 @@
  */
 #include <tvm/data_layout.h>
 #include <tvm/ir_pass.h>
+#include <cctype>
 
 namespace tvm {
 
@@ -115,7 +116,7 @@ Layout::Layout(const std::string& name) { // NOLINT(*)
     char axis = v->var.get()->name_hint[0];
     if (axis >= 'a' && axis <= 'z') {
       CHECK(exist_axis[axis-'a'+'A']) << "Invalid layout " << name << ": missing axis "
-                                      << axis - 'a' + 'A';
+                                      << std::toupper(axis);
     }
   }
 }