[PATCH] Bug in MM_RB debugging

The code is seemingly trying to make sure that rb_next() brings us to
successive increasing vma entries.

But the two variables, prev and pend, used to perform these checks, are
never advanced.

Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Andrea Arcangeli <andrea@novell.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>