direct_dma_ops is the default pci dma ops.

No need to call a function to get the pci dma ops, we know they are the
dma_direct_ops.
Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>