kernel-doc: fix for vunmap function prototype

Fix kernel-doc function prototype parsing which was exposed by vunmap() by
allowing more than one '*' before the function name.

Error(linux-2.6.24-mm1//mm/vmalloc.c:438): cannot understand prototype: 'struct page **vunmap(const void *addr) '

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>