net:enetc: allocate CBD ring data memory using DMA coherent methods

To replace the dma_map_single() stream DMA mapping with DMA coherent
method dma_alloc_coherent() which is more simple.

dma_map_single() found by Tim Gardner not proper. Suggested by Claudiu
Manoil and Jakub Kicinski to use dma_alloc_coherent(). Discussion at:

https://lore.kernel.org/netdev/AM9PR04MB8397F300DECD3C44D2EBD07796BD9@AM9PR04MB8397.eurprd04.prod.outlook.com/t/

Fixes: 888ae5a3

 ("net: enetc: add tc flower psfp offload driver")
cc: Claudiu Manoil <claudiu.manoil@nxp.com>
Reported-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Po Liu <po.liu@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>