util: use origin/develop as default upstream branch

The master branch is not in use anymore and it has been
renamed to develop instead

Change-Id: Ib9ea6e137f1b9284fb8147268b8691d002d3f90a
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/67331
Reviewed-by: Richard Cooper <richard.cooper@arm.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

util/maint/list_changes.py

@@ -178,7 +178,7 @@ def _main():
         "--upstream",
         "-u",
         type=str,
-        default="origin/master",
+        default="origin/develop",
         help="Upstream branch for comparison. Default: %(default)s",
     )
     parser.add_argument(

util/maint/show_changes_by_file.py

@@ -94,7 +94,7 @@ def _main():
         "--upstream",
         "-u",
         type=str,
-        default="origin/master",
+        default="origin/develop",
         help="Upstream branch for comparison. Default: %(default)s",
     )
     parser.add_argument(