net: enetc: pass bd_count as an argument to enetc_setup_cbdr

It makes no sense from an API perspective to first initialize some
portion of struct enetc_cbdr outside enetc_setup_cbdr, then leave that
function to initialize the rest. enetc_setup_cbdr should be able to
perform all initialization given a zero-initialized struct enetc_cbdr.

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