media: atomisp: Rework asd->streaming state update in __atomisp_streamoff()

During the first __atomisp_streamoff() call on an asd with only one pipe
streaming asd->streaming would get set twice:

asd->streaming = ATOMISP_DEVICE_STREAMING_STOPPING;
asd->streaming = ATOMISP_DEVICE_STREAMING_DISABLED;

Rework the code a bit so that it gets set to the correct value
right away instead of doing this in 2 steps.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>