The driver should pass a device that specifies internal DMA ops, but
currently NULL pointer is passed, therefore following bug appears
during boot up:

  ------------[ cut here ]------------
  Kernel BUG at c0018a7c [verbose debug info unavailable]
  Oops: Exception in kernel mode, sig: 5 [#1]
  [...]
  NIP [c0018a7c] fsl_rio_doorbell_init+0x34/0x60
  LR [c0018a70] fsl_rio_doorbell_init+0x28/0x60
  Call Trace:
  [ef82bda0] [c0018a70] fsl_rio_doorbell_init+0x28/0x60 (unreliable)
  [ef82bdc0] [c0019160] fsl_rio_setup+0x6b8/0x84c
  [ef82be20] [c02d28ac] fsl_of_rio_rpn_probe+0x30/0x50
  [ef82be40] [c0234f20] of_platform_device_probe+0x5c/0x84
  [...]
  ---[ end trace 561bb236c800851f ]---

This patch fixes the issue.
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>