rutabaga_gfx: rutabaga_gralloc: fix Kokoro unhappiness
rutabaga_gfx: rutabaga_gralloc: fix Kokoro unhappiness

Should fix the following error:

---- rutabaga_gralloc::gralloc::tests::create_render_target stdout ----
thread 'main' panicked at 'called `Result::unwrap()` on an `Err`
value: Unsupported', rutabaga_gfx/src/rutabaga_gralloc/gralloc.rs:314:64
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

BUG=b:173630595
TEST=cargo test locally

Change-Id: Ieb24166f3975d4d7c99c08a3d0824ee64668c93e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2675231
Tested-by: Gurchetan Singh <99434bba058e25b6203b8ae055a4f697dad0ef64@chromium.org>
Commit-Queue: Gurchetan Singh <99434bba058e25b6203b8ae055a4f697dad0ef64@chromium.org>
Reviewed-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm