disable perform in GpuMultinomialFromUniform as it don't work.

theano/sandbox/multinomial.py

@@ -175,6 +175,12 @@ class GpuMultinomialFromUniform(MultinomialFromUniform, GpuOp):
                     'self.odtype == pvals.dtype', odtype, pvals.dtype)
         return Apply(self, [pvals, unis], [pvals.type()])
 
+    def perform(self, node, ins, outs):
+        #The perform from parent don't work with CudaNdarray.  We
+        #don't need it as DebugMode will test again it as an
+        #optimization insert the GPU op.
+        return Op.perform(self, node, ins, outs)
+
     def c_code_cache_version(self):
         return (8,)