enic: reduce ioread in devcmd2

posted_index is RO in firmware. We need not do ioread everytime to get
posted index. Store posted index locally.

Signed-off-by: Govindarajulu Varadarajan <_govind@gmx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc drivers/net/ethernet/cisco/enic/vnic_dev.c
Simple merge

diff --cc drivers/net/ethernet/cisco/enic/vnic_wq.h
Simple merge