pinctrl: baytrail: consolidate common mask operation

Consolidate common mask operation outside of switch cases and
limit IO operations to positive cases.

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