platform/x86: asus-wmi: fix screenpad brightness range

platform/x86: asus-wmi: fix screenpad brightness range

Fix screenpad brightness range being too limited without reason:
testing this patch on a Zenbook Duo showed the hardware minimum not being
too low, therefore allow the user to configure the entire range, and
expose to userspace the hardware brightness range and value.

Fixes: 2c97d3e55b70 ("platform/x86: asus-wmi: add support for ASUS screenpad")
Signed-off-by: Denis Benato <denis.benato@linux.dev>
Signed-off-by: Luke Jones <luke@ljones.dev>
Link: https://patch.msgid.link/20260302174431.349816-3-denis.benato@linux.dev
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>