pinctrl: intel: Constify struct intel_pinctrl parameter

There are a few functions that do not and should not change
the state of the pin control object. Constify the respective
parameter.

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