[Performance] Remove unnecessary zero-fill of MLA decode output tensor in Aiter backend (#37539)

Signed-off-by: xaguilar-amd <xaguilar@amd.com>

vllm/v1/attention/backends/mla/rocm_aiter_mla.py

@@ -416,7 +416,7 @@ class AiterMLAImpl(MLACommonImpl[AiterMLAMetadata]):
         else:
             kernel_num_heads = self.num_heads
 
-        o = torch.zeros(
+        o = torch.empty(
             B,
             kernel_num_heads,
             self.kv_lora_rank,