net/enic: fix Rx scatter with multiple queues

The Rx scatter patch failed to make a few changes and resulted in
problems when using multiple receive queues (RQs) in DPDK (ie RSS)
since the wrong adapter resources were being used.

- get and use the correct completion queue index associated with a
  receive queue.
- set the correct receive queue index when using RSS

Fixes: 856d7ba7ed22 ("net/enic: support scattered Rx")

Signed-off-by: Nelson Escobar <neescoba@cisco.com>
Reviewed-by: John Daley <johndale@cisco.com>