d_bg_w_kcol work (#2576)

Author: caseif

include/d/d_bg_s_spl_grp_chk.h

@@ -28,7 +28,7 @@ class dBgS_SplGrpChk : public cBgS_PolyInfo, public cBgS_Chk, public dBgS_Chk {
     void SetHeight(f32 height) { m_height = height; }
     f32 GetHeight() { return m_height; }
     cXyz& GetPosP() { return m_ground; }
-    f32 GetRoof() const { return m_roof; }
+    f32 GetRoof() { return m_roof; }
 
 private:
     /* 0x3C */ cXyz m_ground;