static-checks: use origin/master instead of master as base branch

In some CI testing scenarios, there are no local branches, just remotes, so
as a safer approach, use 'origin/master' instead of 'master'. Base
branch is used to find common parent ancestor between
base (origin/master) and user patchset's (FETCH_HEAD) branches.

Change-Id: I36940ac043f45bda6b94e8787b29f319a5f4acba
Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>
diff --git a/script/static-checks/check-include-order.py b/script/static-checks/check-include-order.py
index 4f605f3..6a3a5a3 100755
--- a/script/static-checks/check-include-order.py
+++ b/script/static-checks/check-include-order.py
@@ -223,7 +223,7 @@
     parser.add_argument(
         "--from-ref",
         help="Base commit in patch mode (default: %(default)s)",
-        default="master",
+        default="origin/master",
     )
     parser.add_argument(
         "--to-ref",