binman: Fix up the _DoTestFile() function -u argument

This should be -u, not -up, since we don't need to preserve the output
directory in this case.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/binman/ftest.py

@@ -208,7 +208,7 @@ class TestFunctional(unittest.TestCase):
         if map:
             args.append('-m')
         if update_dtb:
-            args.append('-up')
+            args.append('-u')
         if not use_real_dtb:
             args.append('--fake-dtb')
         if verbosity is not None: