tools/pygrub: Fix a typo handling device specs with no partition part

pygrub: fix a typo that causes exceptions when looking at device
specifications that don't have a partition part (e.g. (hd0)).

Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com>

tools/pygrub/src/GrubConf.py

@@ -61,7 +61,7 @@ class GrubDiskPart(object):
         if self.part is not None:
             return "d%dp%d" %(self.disk, self.part)
         else:
-            return "d%d" %(self,disk,)
+            return "d%d" %(self.disk,)
 
     def get_disk(self):
         return self._disk