mux: gpio: Use bitmap API instead of direct assignment

Assigning bitmaps like it's done in the driver might be error prone.
Fix this by using bitmap API.

Acked-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210330193325.68362-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>