net: ena: fix warning in rmmod caused by double iounmap

Memory mapped with devm_ioremap is automatically freed when the driver
is disconnected from the device. Therefore there is no need to
explicitly call devm_iounmap.

Fixes: 0857d92f ("net: ena: add missing unmap bars on device removal")
Fixes: 411838e7 ("net: ena: fix rare kernel crash when bar memory remap fails")
Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>