drm/i915/gvt: Initialize intel_gvt_gtt_entry in stack

Stack struct intel_gvt_gtt_entry value needs to be initialized before
being used, as the fields may contain garbage values.

W/o this patch, set_ggtt_entry prints:
-------------------------------------
274.046840: set_ggtt_entry: vgpu1:set ggtt entry 0x9bed8000ffffe900
274.046846: set_ggtt_entry: vgpu1:set ggtt entry 0xe55df001
274.046852: set_ggtt_entry: vgpu1:set ggtt entry 0x9bed8000ffffe900

0x9bed8000 is the stack grabage.

W/ this patch, set_ggtt_entry prints:
------------------------------------
274.046840: set_ggtt_entry: vgpu1:set ggtt entry 0xffffe900
274.046846: set_ggtt_entry: vgpu1:set ggtt entry 0xe55df001
274.046852: set_ggtt_entry: vgpu1:set ggtt entry 0xffffe900

v2:
- Initialize during declaration. (Zhenyu)

Fixes: 7598e870 ("drm/i915/gvt: Missed to cancel dma map for ggtt entries")
Cc: stable@vger.kernel.org # v4.20+
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Tina Zhang <tina.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

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

@@ -2183,7 +2183,8 @@ static int emulate_ggtt_mmio_write(struct intel_vgpu *vgpu, unsigned int off,
 	struct intel_gvt_gtt_pte_ops *ops = gvt->gtt.pte_ops;
 	unsigned long g_gtt_index = off >> info->gtt_entry_size_shift;
 	unsigned long gma, gfn;
-	struct intel_gvt_gtt_entry e, m;
+	struct intel_gvt_gtt_entry e = {.val64 = 0, .type = GTT_TYPE_GGTT_PTE};
+	struct intel_gvt_gtt_entry m = {.val64 = 0, .type = GTT_TYPE_GGTT_PTE};
 	dma_addr_t dma_addr;
 	int ret;
 	struct intel_gvt_partial_pte *partial_pte, *pos, *n;
@@ -2250,7 +2251,8 @@ static int emulate_ggtt_mmio_write(struct intel_vgpu *vgpu, unsigned int off,
 
 	if (!partial_update && (ops->test_present(&e))) {
 		gfn = ops->get_pfn(&e);
-		m = e;
+		m.val64 = e.val64;
+		m.type = e.type;
 
 		/* one PTE update may be issued in multiple writes and the
 		 * first write may not construct a valid gfn