can: CAN_MCP251X should depend on HAS_DMA

When building for Sun 3:

drivers/net/can/mcp251x.c:1074: undefined reference to `dma_free_coherent'
drivers/net/can/mcp251x.c:976: undefined reference to `dma_alloc_coherent'
drivers/net/can/mcp251x.c:1050: undefined reference to `dma_free_coherent'

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: David S. Miller <davem@davemloft.net>