regulator: Rename files for max77686 and max77802 drivers

The max77686 and max77802 regulator drivers are for sub-devices of a MFD
driver for some PMIC blocks. But the same object file name (max77686.o)
was used for both the common MFD driver and the max77686 regulator one.

This confuses kbuild if both drivers are built as module causing the MFD
driver to not be copied when installing the modules.

Also, max77{686,802} are a quite generic name for MFD subdevices drivers
so it is better to rename them to max77{686,802}-regulator like it's the
case for most regulator drivers.

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