Fix missed call to is_triton_available

bitsandbytes/nn/triton_based_modules.py

@@ -162,7 +162,7 @@ def __init__(
         ):
         super().__init__(in_features, out_features, bias, device, dtype)
 
-        if not is_triton_available:
+        if not is_triton_available():
             raise ImportError('''Could not import triton. Please install triton to use SwitchBackLinear.
                                Alternatively, you can use bnb.nn.SwitchBackLinearBnb, but it will be slower''')