s5p-mfc: Fix kernel warning on memory init

s5p-mfc: Fix kernel warning on memory init

<UPSTREAM MERGE NOT REQUIRED>

linux-media commit 6e83e6e25eb49dc57a69b3f8ecc1e764c9775101
Original commit message as follows:

  Cleaned up the memory devices allocation code and added
  missing device_initialize() call to remove the kernel warning
  during memory allocations.

  Signed-off-by: Arun Kumar K <arun.kk@samsung.com>
  Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
  Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Change-Id: Ie9cf1d8fcdc3e70acf23329449c8985eab5cd68e
Signed-off-by: John Sheu <sheu@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/45100