[media] atomisp: Unify load_preview_binaries for the most part

ISP2401 introduced a rather sensible change to cut through the structure
spaghetti. Adopt that for the ISP2400 as well. It makes no difference to the
actual code other than readability.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>