media: pxa_camera: declare variable when DEBUG is defined

When DEBUG is defined this error occurs

drivers/media/platform/pxa_camera.c:1410:7: error:
  ‘i’ undeclared (first use in this function)
  for (i = 0; i < vb->num_planes; i++)
       ^
The variable 'i' is missing, so declare it.

Fixes: 6f28435d ("[media] media: platform: pxa_camera: trivial move of functions")
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>