net: enetc: save the DMA device for enetc_free_cbdr

We shouldn't need to pass the struct device *dev to enetc CBDR APIs over
and over again, so save this inside struct enetc_cbdr::dma_dev and avoid
calling it from the enetc_free_cbdr functions.

This breaks the dependency of the cbdr API from struct enetc_si (the
station interface).

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