platform/x86: uniwill-laptop: Properly initialize charging threshold

platform/x86: uniwill-laptop: Properly initialize charging threshold

The EC might initialize the charge threshold with 0 to signal that
said threshold is uninitialized. Detect this and replace said value
with 100 to signal the EC that we want to take control of battery
charging. Also set the threshold to 100 if the EC-provided value
is invalid.

Fixes: d050479693bb ("platform/x86: Add Uniwill laptop driver")
Reviewed-by: Werner Sembach <wse@tuxedocomputers.com>
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://patch.msgid.link/20260512232145.329260-2-W_Armin@gmx.de
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>