pinctrl: lynxpoint: Use defined constant for disabled bias explicitly

We have a specific constant to describe a disabled bias,
i.e. GPIWP_NONE. Use it explicitly instead of making
an assumption about its value.

While at it, move argument assignment to the switch-case
in lp_pin_config_get().

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