LU-6215 llite: handle removal of ki_nbytes in struct kiocb

Starting in kernel version 3.19 the ki_nbytes field was
removed from struct kiocb since now that data can be
extracted from the struct bio_iter data.

Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Change-Id: Iaaf0c6dac19cffb4f4b6fc7a55cbc98cd09678a5
Reviewed-on: http://review.whamcloud.com/14683
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: frank zago <fzago@cray.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>