virtio: video: Add an Error implementation for TryFromFormatError.
virtio: video: Add an Error implementation for TryFromFormatError.

As a convention, error types should always implement Error, so we're
doing it here.

The traits are manually implemented as opposed to using ThisError; it
was simple enough, and using ThisError requires making the error type an
enum which makes it more verbose to construct.

BUG=None
TEST=cargo build --features "video-decoder,ffmpeg"

Change-Id: If94926c1b2f14295b29c877c2c70d361b4adee90
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/3925332
Commit-Queue: Alexandre Courbot <301cd6a3ea50a894b4b51e385c5eb12b9a4ffc0c@chromium.org>
Reviewed-by: Alexandre Courbot <301cd6a3ea50a894b4b51e385c5eb12b9a4ffc0c@chromium.org>

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