net/e1000: fix memory barrier usage in Tx

net/e1000: fix memory barrier usage in Tx

Use rte_cio_wmb instead of rte_wmb when writing TX descriptor since it's
CIO memory.
Replace rte_io_wmb and E1000_PCI_REG_WRITE_RELAXED with
E1000_PCI_REG_WRITE since it has rte_io_wmb inside, which will be more
clear.

Fixes: 1fc9701238ed ("net/e1000: fix i219 hang on reset/close")
Cc: stable@dpdk.org
Signed-off-by: Xiao Zhang <xiao.zhang@intel.com>
Reviewed-by: Gavin Hu <gavin.hu@arm.com>
Reviewed-by: Xiaolong Ye <xiaolong.ye@intel.com>