list.h: fix fatal kernel-doc error

Fix fatal multi-line kernel-doc error in list.h:
function short description must be on one line.

Error(linux-2.6.27-rc2-git3//include/linux/list.h:318): duplicate section name 'Description'

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