stdlib: Fix checkpoint setting through set_workload func

Due to a typo ('checkpoint_dir' instead of 'checkpoint'), setting
checkpoints via the set_workload functions was not working. This patch
fixes this error.

Change-Id: I5720406f2a01f166666e80079c1f84651f750fe2
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/68277
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
diff --git a/src/python/gem5/components/boards/se_binary_workload.py b/src/python/gem5/components/boards/se_binary_workload.py
index dc54257..2558ce3 100644
--- a/src/python/gem5/components/boards/se_binary_workload.py
+++ b/src/python/gem5/components/boards/se_binary_workload.py
@@ -111,16 +111,16 @@
         # Set whether to exit on work items for the se_workload
         self.exit_on_work_items = exit_on_work_items
 
-        # Here we set `self._checkpoint_dir`. This is then used by the
+        # Here we set `self._checkpoint`. This is then used by the
         # Simulator module to setup checkpoints.
         if checkpoint:
             if isinstance(checkpoint, Path):
                 self._checkpoint = checkpoint
             elif isinstance(checkpoint, AbstractResource):
-                self._checkpoint_dir = Path(checkpoint.get_local_path())
+                self._checkpoint = Path(checkpoint.get_local_path())
             else:
                 raise Exception(
-                    "The checkpoint_dir must be None, Path, or "
+                    "The checkpoint must be None, Path, or "
                     "AbstractResource."
                 )