staging/lustre: kiocb->ki_left is removed

We also missed ki_nbytes...

Cc: Kent Overstreet <koverstreet@google.com>
Cc: Andreas Dilger <andreas.dilger@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Peng Tao <tao.peng@emc.com>
Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>