Fix for multi-GPU WAN inference (#10997)

Ensure that hidden_state and shift/scale are on the same device when running with multiple GPUs

Co-authored-by: Jimmy <39@🇺🇸.com>

Author: AmericanPresidentJimmyCarter

src/diffusers/models/transformers/transformer_wan.py

@@ -441,6 +441,14 @@ def forward(
 
         # 5. Output norm, projection & unpatchify
         shift, scale = (self.scale_shift_table + temb.unsqueeze(1)).chunk(2, dim=1)
+
+        # Move the shift and scale tensors to the same device as hidden_states.
+        # When using multi-GPU inference via accelerate these will be on the
+        # first device rather than the last device, which hidden_states ends up
+        # on.
+        shift = shift.to(hidden_states.device)
+        scale = scale.to(hidden_states.device)
+
         hidden_states = (self.norm_out(hidden_states.float()) * (1 + scale) + shift).type_as(hidden_states)
         hidden_states = self.proj_out(hidden_states)