media: s5p-mfc: fix possible null-pointer dereference in s5p_mfc_probe()

The variable pdev is assigned to dev->plat_dev, and dev->plat_dev is
checked in:
  if (!dev->plat_dev)

This indicates both dev->plat_dev and pdev can be NULL. If so, the
function dev_err() is called to print error information.
  dev_err(&pdev->dev, "No platform data specified\n");

However, &pdev->dev is an illegal address, and it is dereferenced in
dev_err().

To fix this possible null-pointer dereference, replace dev_err() with
mfc_err().

Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
Signed-off-by: Tuo Li <islituo@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>