raw/ntb: fix write memory barrier

raw/ntb: fix write memory barrier

All buffers and ring info should be written before tail register update.
This patch relocates the write memory barrier before updating tail register
to avoid potential issues.

Fixes: 11b5c7daf019 ("raw/ntb: add enqueue and dequeue functions")
Cc: stable@dpdk.org
Signed-off-by: Xiaoyun Li <xiaoyun.li@intel.com>
Reviewed-by: Gavin Hu <gavin.hu@arm.com>
Acked-by: Jingjing Wu <jingjing.wu@intel.com>