regulator: max77686: fix gpio_enabled shift wrapping bug

The code should handle more than 32 bits here because "id"
can be a value up to MAX77686_REGULATORS (currently 34).

Convert the gpio_enabled type to DECLARE_BITMAP and use
test_bit/set_bit.

Fixes: 3307e902 ("regulator: max77686: Add GPIO control")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Joe Perches <joe@perches.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org