LU-487 brw_[read|write] stats to correctly counts number of pages.

LU-487 brw_[read|write] stats to correctly counts number of pages.

brw_[read|write] now correctly counts the number of pages. Before
this change, the number of pages multiplied by the page size was
counted.

Change-Id: I069c18cf46c67285de1ae2afc48f7fb4ab92df3c
Signed-off-by: Richard Henwood <rhenwood@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/1056
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>