net: sh_eth: don't use NULL as "struct device" for the DMA mapping API

Using NULL as argument for the DMA mapping API is bogus, as the DMA
mapping API may use information from the "struct device" to perform
the DMA mapping operation. Therefore, pass the appropriate "struct
device".

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: David S. Miller <davem@davemloft.net>