net/ena/base: remove mmiowb not defined macro
net/ena/base: remove mmiowb not defined macro

As there is no replacement for mmiowb() and there is no need to use both
versions in the DPDK, this ifdef was simply removed.

Signed-off-by: Michal Krawczyk <a91dcbb4df49d8bfe0a9930d7ff911a4292ca1f5@semihalf.com>
Reviewed-by: Igor Chauskin <a8d4b4819272c1df83ebe995beed3305455c3333@amazon.com>
Reviewed-by: Guy Tzalik <2e660552b21bf06b7025c5200bbf74d8c7c74097@amazon.com>
Reviewed-by: Stephen Hemminger <06fa905d7f2aaced6dc72e9511c71a2a51e8aead@networkplumber.org>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk