Remove the struct atomisp_sub_device.

This was used for 2 things:

1. In dev_dbg() messages
2. To set the name of the v4l2_subdev for each struct atomisp_sub_device

Now that only 1 subdev is used neither is useful anymore. Remove the _%d
postfix from the v4l2_subdev name and remove the logging of the asd index
from the dev_dbg() messages.

In case of the atomisp_s_input() check to see if an input/sensor has
already been assigned to another subdev the entire check no longer
makes sense, so instead of changing the dev_err() message there just
drop the entire check.
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>