Since commit 297c5eee ("mm: make the vma list be doubly linked") made
it a doubly linked list, we don't need to scan the list when deleting
@vma.

And the original code didn't update the prev pointer. Fix it too.
Signed-off-by: NNamhyung Kim <namhyung@gmail.com>
Acked-by: NGreg Ungerer <gerg@uclinux.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>