binman: Separate out testSplBssPad()

At present this test runs binman twice, which means that the temporary
files from the first run do not get cleaned up. Split this into two tests
to fix this problem.

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

tools/binman/ftest.py

@@ -1022,10 +1022,12 @@ class TestFunctional(unittest.TestCase):
         data = self._DoReadFile('47_spl_bss_pad.dts')
         self.assertEqual(U_BOOT_SPL_DATA + (chr(0) * 10) + U_BOOT_DATA, data)
 
+    def testSplBssPadMissing(self):
+        """Test that a missing symbol is detected"""
         with open(self.TestFile('u_boot_ucode_ptr')) as fd:
             TestFunctional._MakeInputFile('spl/u-boot-spl', fd.read())
         with self.assertRaises(ValueError) as e:
-            data = self._DoReadFile('47_spl_bss_pad.dts')
+            self._DoReadFile('47_spl_bss_pad.dts')
         self.assertIn('Expected __bss_size symbol in spl/u-boot-spl',
                       str(e.exception))