fix(cluster-gan): `valid` shape error

[miaobuao]

reproduct

python ./JGAN/models/cluster_gan/clustergan.py -b 64

error

Traceback (most recent call last):
  File "./cluster_gan.py", line 396, in <module>
    real_loss = bce_loss(D_real, valid)
  File "/usr/local/lib/python3.8/dist-packages/jittor/__init__.py", line 1172, in __call__
    return self.execute(*args, **kw)
  File "/usr/local/lib/python3.8/dist-packages/jittor/nn.py", line 487, in execute
    return bce_loss(output, target, self.weight, self.size_average)
  File "/usr/local/lib/python3.8/dist-packages/jittor/nn.py", line 409, in bce_loss
    loss = - (target * jt.log(jt.maximum(output, 1e-20)) + (1 - target) * jt.log(jt.maximum(1 - output, 1e-20)))
RuntimeError: Wrong inputs arguments, Please refer to examples(help(jt.__mul__)).

Types of your inputs are:
 self   = Var,
 b      = Var,

The function declarations are:
 VarHolder* multiply(VarHolder* x, VarHolder* y)

Failed reason:[f 0422 19:43:25.634921 80 binary_op.cc:432] Check failed xshape(64) == yshape(32) Shape not match, x:float32[64,1,]  y:float32[32,1,]