Instead of relying on the now removed NULL argument to
pci_alloc_consistent, switch to the generic DMA API, and store the struct
device so that we can pass it.

Fixes: 4167b2ad ("PCI: Remove NULL device handling from PCI DMA API")
Reported-by: Matthew Whitehead <tedheadster@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Matthew Whitehead <tedheadster@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>