hdl.ast: Value.matches() with no arguments should return C(1).

The behavior of the following must be always the same:
- `with m.Switch(v): with m.Case(*pats):`
- `with m.If(v.matches(*pats)):`

tests/test_hdl_ast.py

@@ -599,7 +599,7 @@ class OperatorTestCase(FHDLTestCase):
 
     def test_matches(self):
         s = Signal(4)
-        self.assertRepr(s.matches(), "(const 1'd0)")
+        self.assertRepr(s.matches(), "(const 1'd1)")
         self.assertRepr(s.matches(1), """
         (== (sig s) (const 1'd1))
         """)