cnic: Use dma_alloc_coherent().

Replace pci_alloc_consistent() with dma_alloc_coherent() so that
appropriate GFP flags can be used.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: Benjamin Li <benli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>