kernel-doc: add support for one line inline struct member doc comments

kernel-doc supports documenting struct members "inline" since
a4c6ebed ("scripts/kernel-doc Allow struct arguments documentation
in struct body"). This requires the inline kernel-doc comments to have
the opening and closing comment markers (/** and */ respectively) on
lines of their own, even for short comments. For example:

	/**
	 * struct foo - struct documentation
	 */
	struct foo {
		/**
		 * @bar: member documentation
		 */
		int bar;
	};

Add support for one line inline comments:

	/**
	 * struct foo - struct documentation
	 */
	struct foo {
		/** @bar: member documentation */
		int bar;
	};

Note that mixing of the two in one doc comment is not allowed; either
both comment markers must be on lines of their own, or both must be on
the one line. This limitation keeps both the comments more uniform, and
kernel-doc less complicated.

Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>