pinctrl: intel: Constify intel_get_community() returned object

There is nothing prevents us from constifying intel_get_community()
returned object. Do it to make code more robust.

Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>