Update doc/developer-guides/hld/hld-devicemodel.rst

Co-Authored-By: dbkinder <david.b.kinder@intel.com>

Author: Geoffroy Van Cutsem

doc/developer-guides/hld/hld-devicemodel.rst

@@ -301,7 +301,7 @@ G, gvtargs <GVT_args>
 
    Where:
 
-   - gvt_high_gm_sz: GVT-g aperture size, unit is MB
+   - ``gvt_high_gm_sz``: GVT-g aperture size, unit is MB
    - gvt_low_gm_sz: GVT-g hidden gfx memory size, unit is MB
    - gvt_fence_sz: the number of fence registers