scripts: kernel-doc: fix parsing function-like typedefs

Changeset 6b80975c6308 ("scripts: kernel-doc: fix typedef parsing")
added support for things like:

typedef unsigned long foo();

However, it caused a regression on this prototype:

typedef bool v4l2_check_dv_timings_fnc(const struct v4l2_dv_timings *t, void *handle);

This is only noticed after adding a patch that checks if the
kernel-doc identifier matches the typedef:

./scripts/kernel-doc -none $(git grep '^.. kernel-doc::' Documentation/ |cut -d ' ' -f 3|sort|uniq) 2>&1|grep expecting
include/media/v4l2-dv-timings.h:38: warning: expecting prototype for typedef v4l2_check_dv_timings_fnc. Prototype was for typedef nc instead

The problem is that, with the new parsing logic, it is not
checking for complete words at the type part.

Fix it by adding a \b at the end of each type word at the
regex.

fixes: 6b80975c6308 ("scripts: kernel-doc: fix typedef parsing")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/218ff56dcb8e73755005d3fb64586eb1841a276b.1606896997.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>