aries | p1: writeback: account NR_WRITTEN at IO completion time

NR_WRITTEN is now accounted at block IO enqueue time, which is not very
accurate as to common understanding.  This moves NR_WRITTEN accounting to
the IO completion time and makes it more consistent with BDI_WRITTEN,
which is used for bandwidth estimation.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Michael Rubin <mrubin@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Change-Id: I6c36b614c7af4d21b4c948d4d6165f1f1edac047
Merge "aries | p1: writeback: account NR_WRITTEN at IO completion time" into android-4.4