fix EleutherAI/gpt-neox-20b does not work in tgi (#2346)

Signed-off-by: Wang, Yi A <yi.a.wang@intel.com>

server/text_generation_server/models/custom_modeling/flash_neox_modeling.py

@@ -153,8 +153,16 @@ class FlashNeoxAttention(torch.nn.Module):
         qkv = self.query_key_value(hidden_states)
         qkv = qkv.view(-1, 3, self.num_heads, self.head_size)
 
+        # Compute rotary embeddings on rotary_ndims
+        query_rot = qkv[:, 0][..., : self.rotary_dim]
+        query_pass = qkv[:, 0][..., self.rotary_dim :]
+        key_rot = qkv[:, 1][..., : self.rotary_dim]
+        key_pass = qkv[:, 1][..., self.rotary_dim :]
+
         # Inplace rotary
-        self.rotary_emb(qkv[:, 0], qkv[:, 1], cos, sin)
+        self.rotary_emb(query_rot, key_rot, cos, sin)
+        qkv[:, 0] = torch.cat((query_rot, query_pass), dim=-1)
+        qkv[:, 1] = torch.cat((key_rot, key_pass), dim=-1)
 
         reshape_and_cache(qkv[:, 1], qkv[:, 2], kv_cache[0], kv_cache[1], slots)