Fix cargo doc for staging

[alyssais]

Summary of the PR

Requirements

Before submitting your PR, please make sure you addressed the following
requirements:

• All commits in this PR have Signed-Off-By trailers (with
  git commit -s), and the commit message has max 60 characters for the
  summary and max 75 characters for each description line.
• All added/changed functionality has a corresponding unit/integration
  test.
• All added/changed public-facing functionality has entries in the "Upcoming
  Release" section of CHANGELOG.md (if no such section exists, please create one).
• Any newly added unsafe code is properly documented.

[stefano-garzarella]

What about using `` for the path?
I mean this:

Suggested change

	/// Create a new virtio video device for /dev/video\<num>.
	/// Create a new virtio video device for `/dev/video<num>`.

[alyssais]

Personally I find documentation easier to read when it exercises restraint with inline code formatting, but as long as it's consistent, it's fine. I've updated the PR to consistently mark up paths in documentation as code.