code_size_compare: left align file names in markdown table

Signed-off-by: Yanray Wang <yanray.wang@arm.com>
diff --git a/scripts/code_size_compare.py b/scripts/code_size_compare.py
index 55d116e..4642906 100755
--- a/scripts/code_size_compare.py
+++ b/scripts/code_size_compare.py
@@ -625,7 +625,7 @@
                              "change(text,data)", "change%(text,data)"))
         if with_markdown:
             output.write(format_string
-                         .format("----:", "----:", "----:", "----:", "----:"))
+                         .format(":----", "----:", "----:", "----:", "----:"))
 
         for mod, fname, size_entry in \
                 self._size_reader_helper(new_rev, output, with_markdown):