gpio: wcove: use regmap_assign_bits() for conditional set/clear

Replace if/else block using regmap_set_bits()/regmap_clear_bits() with
the simpler regmap_assign_bits() call.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>