power: reset: gpio-poweroff: Clarify the warning message

power: reset: gpio-poweroff: Clarify the warning message

When gpio-poweroff fails, a WARN_ON() is triggered without
an explanation to the user about the failure.

Add some comments explaining that the attempt to poweroff the system
via gpio-poweroff failed and convert it to a WARN() message with a
bit of context to provide some hint to the user.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20241212130456.580197-1-festevam@gmail.com
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>