drm/i915/gvt: correct mask setting for CSFE_CHICKEN1

CSFE_CHICKEN1(0x20d4) needs access with mask. This is caught in AcrnGT
conformance check test:

[drm:intel_gvt_vgpu_conformance_check]
	*ERROR* gvt: vgpu1 unconformance mmio 0x20d4:0x40004,0x4

Signed-off-by: Xinyun Liu <xinyun.liu@intel.com>
Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

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

@@ -144,7 +144,7 @@ static struct engine_mmio gen9_engine_mmio_list[] __cacheline_aligned = {
 	{RCS, GAMT_CHKN_BIT_REG, 0x0, false}, /* 0x4ab8 */
 
 	{RCS, GEN9_GAMT_ECO_REG_RW_IA, 0x0, false}, /* 0x4ab0 */
-	{RCS, GEN9_CSFE_CHICKEN1_RCS, 0x0, false}, /* 0x20d4 */
+	{RCS, GEN9_CSFE_CHICKEN1_RCS, 0xffff, false}, /* 0x20d4 */
 
 	{RCS, GEN8_GARBCNTL, 0x0, false}, /* 0xb004 */
 	{RCS, GEN7_FF_THREAD_MODE, 0x0, false}, /* 0x20a0 */