scripts/tags.sh: fix DEFINE_HASHTABLE in emacs case

The emacs --regex for DEFINE_HASHTABLE produced a warning because of
an unmatched '\('.  Further, the whole entry did not work, because the
regex needs to match from the beginning of a line, including keywords
like 'static'.  Finally, '\w' should not be used, because it
stops at underscores which are often part of variable names in C,
resulting in wrong entries in the tags file.

Signed-off-by: Dirk Gouders <dirk@gouders.net>
Inspired-by: Masatake YAMATO <yamato@redhat.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>