fix gpu target detection again

src/lbmpy/lbstep.py

@@ -47,10 +47,8 @@ class LatticeBoltzmannStep:
         if config is not None:
             if IS_PYSTENCILS_2:
                 target = config.get_target()
-                is_gpu = target.is_gpu()
             else:
                 target = config.target
-                is_gpu = target == Target.GPU
         else:
             target = optimization.get('target', Target.CPU)
 
@@ -93,7 +91,11 @@ class LatticeBoltzmannStep:
         self.density_data_name = name + "_density" if density_data_name is None else density_data_name
         self.density_data_index = density_data_index
 
-        self._gpu = is_gpu
+        if IS_PYSTENCILS_2:
+            self._gpu = target.is_gpu()
+        else:
+            self._gpu = target == Target.GPU
+
         layout = lbm_optimisation.field_layout
 
         alignment = False