[PATCH] lower VM_DONTCOPY total_vm

dup_mmap of a VM_DONTCOPY vma forgot to lower the child's total_vm.  (But
no way does this account for the recent report of total_vm seen too low.)

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>