media: Staging: atomisp: constify driver_attribute

driver_attribute are not supposed to change at runtime.
Functions driver_create_file/driver_remove_file are working with
const driver_attribute. So mark the non-const structs as const.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>