[VAAPI-DRM] Fix GpuMemoryBuffer format when creating a pixmap

Reverting back to using BGRA_8888 format to fix the following errors:
[0204/075331:ERROR:gl_image_linux_dma_buffer.cc(79)] Invalid format:
6408
[0204/075331:ERROR:vaapi_drm_picture.cc(110)] Failed to create GLImage

BUG=447798
TEST=Ran ./video_decode_accelerator_test and verified that the above
error isn't present anymore

Review URL: https://codereview.chromium.org/886353005

Cr-Commit-Position: refs/heads/master@{#314735}

content/common/gpu/media/vaapi_drm_picture.cc

@@ -105,7 +105,7 @@ bool VaapiDrmPicture::Initialize() {
   gfx::ScopedTextureBinder texture_binder(GL_TEXTURE_EXTERNAL_OES,
                                           texture_id());
   gl_image_ = ui::GpuMemoryBufferFactoryOzoneNativeBuffer::CreateImageForPixmap(
-      pixmap_, size(), gfx::GpuMemoryBuffer::RGBA_8888, GL_RGBA);
+      pixmap_, size(), gfx::GpuMemoryBuffer::BGRA_8888, GL_RGBA);
   if (!gl_image_) {
     LOG(ERROR) << "Failed to create GLImage";
     return false;