net: enetc: rename "xdp" and "dev" in enetc_setup_bpf()

Follow the convention from this driver, which is to name "struct
net_device *" as "ndev", and the convention from other drivers, to name
"struct netdev_bpf *" as "bpf".

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>