media/gpu/v4l2: do not use aggregate initializer for v4l2_format

C++ aggregate initializers will only initializer the first member
of a union, which in the case of v4l2_format leaves a lot of data
uninitialized. Fix this by initializing it with memset().

BUG=chromium:1068447
BUG=b:153935975
TEST=VDAtest passes on nyan_kitty.

Change-Id: I7138b49780a9845ea924be00f11ccaa7a6904f6e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2147399Reviewed-by: Miguel Casas <mcasas@chromium.org>
Commit-Queue: Alexandre Courbot <acourbot@chromium.org>
Auto-Submit: Alexandre Courbot <acourbot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758854}

media/gpu/v4l2/v4l2_device.cc

@@ -886,7 +886,8 @@ base::Optional<struct v4l2_format> V4L2Queue::SetFormat(uint32_t fourcc,
 }
 
 std::pair<base::Optional<struct v4l2_format>, int> V4L2Queue::GetFormat() {
-  struct v4l2_format format = {};
+  struct v4l2_format format;
+  memset(&format, 0, sizeof(format));
   format.type = type_;
   if (device_->Ioctl(VIDIOC_G_FMT, &format) != 0) {
     VPQLOGF(2) << "Failed to get format";