media: atomisp: fix VIDIOC_S_FMT logic

There are several issues on S_FMT implementation:

- it doesn't properly handle pad_h/pad_w;
- it reports a wrong visible size to userspace;
- it allows setting the format to a raw mode, which
  currently causes the pipeline to break.

Address such issues, for it to start working with generic
apps.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>