scripts/kernel-doc: parse kernel-doc deterministically

Regular expressions for highlights in kernel-doc are stored in a Perl
hash.  These hashes are ordered differently for each Perl run. This will
prevent kernel-doc to behave deterministically when parsing “@foo()” as
in some runs it will be interpreted as a parameter and in the others it
will be interpreted as a function.

We now sort the %highlights hash to get the same behavior on every run.

Signed-off-by: Jérémy Bobbio <lunar@debian.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>