regulator: max77620: check for valid regulator info

SD4 regulator is not registered with regulator core
framework in probe as there is no support in MAX77620 PMIC,
removing SD4 entry from MAX77620 regulator information list
and checking for valid regulator information data before
configuring FPS source and FPS power up/down period to avoid
NULL pointer exception if regulator not registered with core.

Signed-off-by: Venkat Reddy Talla <vreddytalla@nvidia.com>
Signed-off-by: Mark Brown <broonie@kernel.org>