regulator: bd71828-regulator.c: Fix LDON-HEAD mode

The ROHM BD72720 supports so called LDON-HEAD -mode, in which the buck10
is expected to be supplying power for an LDO. In this mode, the buck10
voltage will follow what is set for the LDO, on order to lower the
power-loss in the LDO.

This hardware configuration can be adverticed via the device-tree. When
this is done, the Linux driver should omit registering the voltage
control operations for the buck10, because the voltage control is now
done by the hardware.

This is done by modifying the buck10 regulator descriptor, before
passing it to the regulator registration functions. There is an
off-by-one error when the regulator descriptor array is indexed, and
wrong descriptor is modified causing the LDO1 operations to be modified
instead of the BUCK10 operations.

Fix this by correcting the indexing.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Fixes: f16a9d76a71d ("regulator: bd71828: Support ROHM BD72720")
Link: https://patch.msgid.link/e7eef0bd407522ae5d9b7d0c4ec43f40b1dba833.1775565148.git.mazziesaccount@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>