documentation: da9052: Update regulator bindings names to match DA9052/53 DTS expectations

Buck and LDO binding name changes.

The binding names for the regulators have been changed to match the current
expectation from existing device tree source files.

This fix rectifies the disparity between what currently exists in some
.dts[i] board files and what is listed in this binding document. This
change re-aligns those differences and also brings the binding document
in-line with the expectations of the product datasheet from Dialog
Semiconductor.

Bucks and LDOs now follow the expected notation:
{ buck1, buck2, buck3, buck4 }
{ ldo1, ldo2, ldo3, ldo4, ldo5, ldo6, ldo7, ldo8, ldo9, ldo10 }

Signed-off-by: Steve Twiss <stwiss.opensource@diasemi.com>
Signed-off-by: Rob Herring <robh@kernel.org>