net: pse-pd: pd692x0: Skip power budget configuration when undefined

If the power supply's power budget is not defined in the device tree,
the current code still requests power and configures the PSE manager
with a 0W power limit, which is undesirable behavior.

Skip power budget configuration entirely when the budget is zero,
avoiding unnecessary power requests and preventing invalid 0W limits
from being set on the PSE manager.

Fixes: 35975401 ("net: pse-pd: pd692x0: Add support for PSE PI priority feature")
Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Acked-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/20250820133321.841054-1-kory.maincent@bootlin.com


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