platform/x86: uniwill-laptop: Accept charging threshold of 0

platform/x86: uniwill-laptop: Accept charging threshold of 0

The power supply sysfs ABI states that:

	Not all hardware is capable of setting this to an arbitrary
	percentage. Drivers will round written values to the nearest
	supported value. Reading back the value will show the actual
	threshold set by the driver.

The driver currently violates this ABI by rejecting a charging
threshold of 0. Fix this by clamping this value to 1.

Fixes: d050479693bb ("platform/x86: Add Uniwill laptop driver")
Reviewed-by: Werner Sembach <wse@tuxedocomputers.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://patch.msgid.link/20260512232145.329260-3-W_Armin@gmx.de
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>