drm/i915/gvt: set default value to 0 for unhandled mmio regs

for a handled mmio reg,  its default value is read from hardware, while
for an unhandled mmio regs,  its default value would be random if not
explicitly set to 0

Signed-off-by: Zhao Yan <yan.y.zhao@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

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

@@ -80,7 +80,7 @@ static int expose_firmware_sysfs(struct intel_gvt *gvt)
 	int ret;
 
 	size = sizeof(*h) + info->mmio_size + info->cfg_space_size - 1;
-	firmware = vmalloc(size);
+	firmware = vzalloc(size);
 	if (!firmware)
 		return -ENOMEM;