dt-bindings: firmware: google,gs101-acpm-ipc: convert regulators to lowercase

dt-bindings: firmware: google,gs101-acpm-ipc: convert regulators to lowercase

Using lowercase for the buck and ldo nodenames is preferred, as
evidenced e.g. in [1].

Convert the example here to lowercase before we add any bindings
describing the s2mpg1x regulators that will enforce the spelling.

Link: https://lore.kernel.org/all/20250223-mysterious-infrared-civet-e5bcbf@krzk-bin/
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: André Draszik <andre.draszik@linaro.org>
Link: https://patch.msgid.link/20260122-s2mpg1x-regulators-v7-1-3b1f9831fffd@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>