[PATCH] list.h doc: change "counter" to "cursor"

Use loop "cursor" instead of loop "counter" for list iterator descriptions.
They are not counters, they are pointers or positions.

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>