drm/i915/gvt: remove useless function

Fix the following clang warning:

drivers/gpu/drm/i915/gvt/gtt.c:590:20: warning: unused function
'ppgtt_set_guest_root_entry' [-Wunused-function].
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1618294728-78952-1-git-send-email-jiapeng.chong@linux.alibaba.comReviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>

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

@@ -587,12 +587,6 @@ static void _ppgtt_set_root_entry(struct intel_vgpu_mm *mm,
 			   entry, index, false, 0, mm->vgpu);
 }
 
-static inline void ppgtt_set_guest_root_entry(struct intel_vgpu_mm *mm,
-		struct intel_gvt_gtt_entry *entry, unsigned long index)
-{
-	_ppgtt_set_root_entry(mm, entry, index, true);
-}
-
 static inline void ppgtt_set_shadow_root_entry(struct intel_vgpu_mm *mm,
 		struct intel_gvt_gtt_entry *entry, unsigned long index)
 {