staging/lustre/llite: use READ, WRITE around ll_rw_stats_tally()

In vvp_io_write_start() the stats function ll_rw_stats_tally() was
incorrectly called with a rw argument of 0. Correct this and use the
macros READ and WRITE in and around ll_rw_stats_tally() for clarity.

Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3384
Lustre-change: http://review.whamcloud.com/6447


Signed-off-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Signed-off-by: Peng Tao <tao.peng@emc.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>