soc: fsl: dpio: read the consumer index from the cache inhibited area

Once we added support in the dpaa2-eth for driver level software TSO we
observed the following situation: if the EQCR CI (consumer index) is
read from the cache-enabled area we sometimes end up with a computed
value of available enqueue entries bigger than the size of the ring.

This eventually will lead to the multiple enqueue of the same FD which
will determine the same FD to end up on the Tx confirmation path and the
same skb being freed twice.

Just read the consumer index from the cache inhibited area so that we
avoid this situation.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>