fix SeqParallelMultiHeadCrossAttention for consistent results in dist…

…ributed mode (#510)

opensora/models/layers/blocks.py

@@ -499,7 +499,7 @@ def forward(self, x, cond, mask=None):
 
  # shape:
  # q, k, v: [B, SUB_N, NUM_HEADS, HEAD_DIM]
- q = self.q_linear(x).view(1, -1, self.num_heads, self.head_dim)
+ q = self.q_linear(x).view(B, -1, self.num_heads, self.head_dim)
  kv = self.kv_linear(cond).view(1, -1, 2, self.num_heads, self.head_dim)
  kv = split_forward_gather_backward(kv, get_sequence_parallel_group(), dim=3, grad_scale="down")
  k, v = kv.unbind(2)