[Bugfix] Add missing activation attr to RMSNormGated (#35423)

Signed-off-by: tibG <naps@qubes.milou>
Co-authored-by: tibG <naps@qubes.milou>

vllm/model_executor/layers/layernorm.py

@@ -510,6 +510,7 @@ class RMSNormGated(CustomOp):
         norm_before_gate: bool = False,
         device: torch.device | None = None,
         dtype: torch.dtype | None = None,
+        activation: str = "swish",
     ):
         """Initialize RMSNormGated.
 
@@ -524,10 +525,12 @@ class RMSNormGated(CustomOp):
                               If False and z is provided: out = norm(x * silu(z))
             device: Device to create parameters on
             dtype: Data type for parameters
+            activation: Activation function name for gating
         """
         factory_kwargs = {"device": device, "dtype": dtype}
         super().__init__()
         self.eps = eps
+        self.activation = activation
         self.weight = nn.Parameter(torch.empty(hidden_size, **factory_kwargs))
         self.register_parameter("bias", None)
         self.group_size = group_size