net: ena: add missing unmap bars on device removal

This patch also change the mapping functions to devm_ functions

Fixes: 1738cd3e

 ("Add a driver for Amazon Elastic Network Adapters (ENA)")
Signed-off-by: Netanel Belgazal <netanel@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>