regulator: max77686: Fix MAINTAINER entry to match driver

The max77686 regulator driver was recently renamed to max77686-regulator
but the entry in the MAINTAINERS file wasn't updated to match the driver.

Reported-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>