binman: Correct a typo in the toolpath comment

Fix the 'ist' typo in the comment for TestFunctional

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/ftest.py b/tools/binman/ftest.py
index fc02e64..d3e6e67 100644
--- a/tools/binman/ftest.py
+++ b/tools/binman/ftest.py
@@ -283,7 +283,7 @@
             preserve_outdir: Preserve the output directories used by tests. Each
                 test has its own, so this is normally only useful when running a
                 single test.
-            toolpath: ist of paths to use for tools
+            toolpath: list of paths to use for tools
         """
         cls.preserve_indir = preserve_indir
         cls.preserve_outdirs = preserve_outdirs