media: atomisp: Change ISP subdev name to "ATOM ISP"

Change the generic "ATOMISP_SUBDEV" name to "ATOM ISP" to make clear
that this is the subdev for the ISP itself.

Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
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>