netdev-dpdk: Remove uneeded call to rte_eth_dev_count().

netdev-dpdk: Remove uneeded call to rte_eth_dev_count().

The call to rte_eth_dev_count() was added as workaround
for rte_eth_dev_get_port_by_name() not handling cases
when there was no DPDK ports.

In versions of DPDK >= 17.02 rte_eth_dev_get_port_by_name()
does handle this case (DPDK commit f9ae888b1e19).
rte_eth_dev_count() is no longer needed so remove it.

Acked-by: Ciara Loftus <ciara.loftus@intel.com>
Signed-off-by: Kevin Traynor <ktraynor@redhat.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>