Fix: Cycles: Rendering of the Principled BSDF when using adaptive kernel compilation

Fixes a issue where the Principled BSDF would render incorrectly if
`__SUBSURFACE__` is off. Which is common when using adaptive kernel
compilation (a unsupported Cycles feature).

Pull Request: https://projects.blender.org/blender/blender/pulls/128003

intern/cycles/kernel/svm/closure.h

@@ -151,9 +151,7 @@ ccl_device
       const float3 clamped_base_color = min(base_color, one_float3());
 
       // get the subsurface scattering data
-#ifdef __SUBSURFACE__
       uint4 data_subsurf = read_node(kg, &offset);
-#endif
 
       uint4 data_alpha_emission_thin = read_node(kg, &offset);
       svm_unpack_node_uchar4(data_alpha_emission_thin.x,
@@ -419,6 +417,7 @@ ccl_device
       }
 #else
       subsurface_weight = 0.0f;
+      (void)data_subsurf;
 #endif
 
       ccl_private OrenNayarBsdf *bsdf = (ccl_private OrenNayarBsdf *)bsdf_alloc(