platform/x86: dell-rbtn: constify rfkill_ops structures

Add const to rfkill_ops structures that are only passed as an argument
to the functions rfkill_alloc or samsung_new_rfkill. These arguments are
of type const, so such structures can be annotated with const.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>