drm/i915/gvt: add vreg write for GDRST handler

The emulation handler for MMIO GDRST miss vreg write in it, as result
the vreg cannot update correspondingly.
Signed-off-by: Ping Gao <ping.a.gao@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/handlers.c

@@ -258,6 +258,7 @@ static int gdrst_mmio_write(struct intel_vgpu *vgpu, unsigned int offset,
 	u32 data;
 	u64 bitmap = 0;
 
+	write_vreg(vgpu, offset, p_data, bytes);
 	data = vgpu_vreg(vgpu, offset);
 
 	if (data & GEN6_GRDOM_FULL) {