Fix ewmh.activate to use the hints argument

This was missed in cb7f4b06, where the `raise` argument was changed to
`hints`.

lib/awful/ewmh.lua

@@ -161,7 +161,7 @@ end
 -- @tparam boolean hints.raise should the client be raised? (default false)
 function ewmh.activate(c, context, hints)
     client.focus = c
-    if raise then
+    if hints.raise then
         if awesome.startup or c:isvisible() then
             c:raise()
         else