shader: initialize perspective sample barycentrics at SampleId

src/graphics/shader/recompiler/frontend/translate/Translate.cpp

@@ -1281,6 +1281,8 @@ IR::Program TranslateProgram(const Decoder::Program& decoded, const CFG::Graph&
 				}
 			};
 			barycentric_pair(ps->ps_perspective_center_vgpr, IR::StageInputKind::BaryCoordSmooth);
+			barycentric_pair(ps->ps_perspective_sample_vgpr,
+			                 IR::StageInputKind::BaryCoordSmoothSample);
 			barycentric_pair(ps->ps_perspective_centroid_vgpr,
 			                 IR::StageInputKind::BaryCoordSmoothCentroid);
 			uint32_t reg = ps->ps_system_input_base;