net: enetc: simplify callers of enetc_rxbd_next

net: enetc: simplify callers of enetc_rxbd_next

When we iterate through the BDs in the RX ring, the software producer
index (which is already passed by value to enetc_rxbd_next) lags behind,
and we end up with this funny looking "++i == rx_ring->bd_count" check
so that we drag it after us.

Let's pass the software producer index "i" by reference, so that
enetc_rxbd_next can increment it by itself (mod rx_ring->bd_count),
especially since enetc_rxbd_next has to increment the index anyway.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>