Fix typo in RotaryEmbedding forward output type (#666)

flash_attn/layers/rotary.py

@@ -417,7 +417,7 @@ class RotaryEmbedding(torch.nn.Module):
         kv: Optional[torch.Tensor] = None,
         seqlen_offset: Union[int, torch.Tensor] = 0,
         max_seqlen: Optional[int] = None,
-    ) -> Tuple[torch.Tensor, torch.Tensor]:
+    ) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
         """
         qkv: (batch, seqlen, 3, nheads, headdim) if kv is none,
              else it's just q of shape (batch, seqlen, nheads, headdim)