regulator: bd71837: Remove duplicate description from DT bindings

Same general chip description was written in MFD and Regulator
binding documents for ROHM bd71837 PMIC. Remove description from
regulator binding as suggested by Rob H.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Signed-off-by: Mark Brown <broonie@kernel.org>