fore200e: devirtualize dma alloc calls

There is no need for an indirection before calling the dma alloc
routines now that we store a struct device in struct fore200e.

Also remove the pointless GFP_ATOMIC for the sbus case, and fix the
up the error handling by removing the 0 dma_addr test - some iommus
can return 0 as a perfectly valid bus address.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>