[Bugfix] Fix Basic Models Test (#34818)

Signed-off-by: Matthew Bonanni <mbonanni@redhat.com>
Co-authored-by: Robert Shaw <114415538+robertgshaw2-redhat@users.noreply.github.com>

vllm/model_executor/layers/attention/mla_attention.py

@@ -407,17 +407,24 @@ class MLAAttention(nn.Module, AttentionLayerBase):
         )
 
         # Attributes for forward_impl method
-        self.chunked_prefill_workspace_size = (
-            MLACommonMetadataBuilder.determine_chunked_prefill_workspace_size(
-                get_current_vllm_config()
-            )
-        )
+        self._vllm_config = get_current_vllm_config()
+        self._chunked_prefill_workspace_size: int | None = None
         self._decode_concat_quant_fp8_op = _DecodeConcatQuantFP8(
             static=True,
             group_shape=GroupShape.PER_TENSOR,
             compile_native=True,
         )
 
+    @property
+    def chunked_prefill_workspace_size(self) -> int:
+        if self._chunked_prefill_workspace_size is None:
+            self._chunked_prefill_workspace_size = (
+                MLACommonMetadataBuilder.determine_chunked_prefill_workspace_size(
+                    self._vllm_config
+                )
+            )
+        return self._chunked_prefill_workspace_size
+
     def forward(
         self,
         q: torch.Tensor,