powerpc/pmac: Fix crash in dma-mapping.h with NULL dma_ops

powerpc/pmac: Fix crash in dma-mapping.h with NULL dma_ops

Commit 5657933dbb6e ("treewide: Move dma_ops from struct dev_archdata
into struct device") introduced a crash for macio devices, an example
backtrace being:

  kernel BUG at ./include/linux/dma-mapping.h:465!
  Oops: Exception in kernel mode, sig: 5 [#1]
  ...
  NIP [c031ddb0] dmam_alloc_coherent+0x74/0x140
  LR [c031de70] dmam_alloc_coherent+0x134/0x140
  Call Trace:
   dmam_alloc_coherent+0x134/0x140 (unreliable)
   pata_macio_port_start+0x3c/0x8c
   ata_host_start.part.5+0xfc/0x208
   ata_host_activate+0x128/0x154
   pata_macio_common_init+0x2f0/0x538
   pata_macio_attach+0xd8/0x180
   macio_device_probe+0x5c/0xec
   driver_probe_device+0x21c/0x314
   __driver_attach+0xcc/0xd0
   bus_for_each_dev+0x68/0xb4
   bus_add_driver+0x1dc/0x244
   driver_register+0x88/0x130
   pata_macio_init+0x5c/0x88
   do_one_initcall+0x40/0x170
   kernel_init_freeable+0x134/0x1d0
   kernel_init+0x18/0x110
   ret_from_kernel_thread+0x5c/0x64

This was caused by the device having NULL dma_ops, triggering the
BUG_ON(). Previously the device inherited its dma_ops via the assignment
to dev->ofdev.dev.archdata. However after commit 5657933dbb6e the
dma_ops are moved into dev->ofdev.dev, and so they need to be explicitly
copied.

Fixes: 5657933dbb6e ("treewide: Move dma_ops from struct dev_archdata into struct device")
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Suggested-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
[mpe: Rewrite change log, add backtrace]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>