kernel-doc: better handle '::' sequences

kernel-doc: better handle '::' sequences

Right now, if one of the following headers end with a '::', the
kernel-doc script will do the wrong thing:

	description|context|returns?|notes?|examples?

The real issue is with examples, as people could try to write
something like:

	example::

		/* Some C code */

and this won't be properly evaluated. So, improve the regex
to not catch '\w+::' regex for the above identifiers.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/2cf44cf1fa42588632735d4fbc8e84304bdc235f.1616696051.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>