net: pse-pd: pse_core: Fix pse regulator type

Clarify PSE regulator as voltage regulator, not current.
The PSE (Power Sourcing Equipment) regulator is defined as a voltage
regulator, maintaining fixed voltage while accommodating varying current.

Fixes: d83e1376 ("net: pse-pd: Use regulator framework within PSE framework")
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Link: https://lore.kernel.org/r/20240423-fix_poe-v3-2-e50f32f5fa59@bootlin.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>