binman: Tidy up comments on _DoTestFile()

The comment for this function is missing an argument and the return value.
Fix it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/ftest.py b/tools/binman/ftest.py
index 8199a4f..39a4b94 100644
--- a/tools/binman/ftest.py
+++ b/tools/binman/ftest.py
@@ -334,6 +334,11 @@
             extra_indirs: Extra input directories to add using -I
             threads: Number of threads to use (None for default, 0 for
                 single-threaded)
+            test_section_timeout: True to force the first time to timeout, as
+                used in testThreadTimeout()
+
+        Returns:
+            int return code, 0 on success
         """
         args = []
         if debug: