Make the random generator work.

theano/sandbox/rng_mrg.py

@@ -771,6 +771,9 @@ class GPUA_mrg_uniform(GpuKernelBase, mrg_uniform_base):
     # GpuArray version
     _f16_ok = True
 
+    def get_context(self, node):
+        return node.inputs[0].type.context
+
     @classmethod
     def new(cls, rstate, ndim, dtype, size):
         v_size = as_tensor_variable(size)