platform/x86: asus-wmi: adjust screenpad power/brightness handling

platform/x86: asus-wmi: adjust screenpad power/brightness handling

Fix illogical screen off control by hardcoding 0 and 1 depending on the
requested brightness and also do not rely on the last screenpad power
state to issue screen brightness commands.

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/20260302174431.349816-2-denis.benato@linux.dev
Link: https://patch.msgid.link/20260326231154.856729-2-ethantidmore06@gmail.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>