media: staging: media: atomisp: Refactor ia_css_stream_load()

Move the support check to the beginning of the function.
Change the logic to avoid multiple nesting blocks.
Move 'err' variable assignment outside of the if statement.
Remove an unnecessary check whether 'j' is zero.

Signed-off-by: Martiros Shakhzadyan <vrzh@vrzh.net>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>