platform/x86: asus-wmi: Fix "unsigned 'retval' is never less than zero" smatch warning

platform/x86: asus-wmi: Fix "unsigned 'retval' is never less than zero" smatch warning

Eliminate the follow smatch warnings:

drivers/platform/x86/asus-wmi.c:478 panel_od_write() warn: unsigned
'retval' is never less than zero.

drivers/platform/x86/asus-wmi.c:566 panel_od_write() warn: unsigned
'retval' is never less than zero.

drivers/platform/x86/asus-wmi.c:1451 panel_od_write() warn: unsigned
'retval' is never less than zero.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Fixes: 98829e84dc67 ("asus-wmi: Add dgpu disable method")
Fixes: 382b91db8044 ("asus-wmi: Add egpu enable method")
Fixes: ca91ea34778f ("asus-wmi: Add panel overdrive functionality")
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Link: https://lore.kernel.org/r/1629887822-23918-1-git-send-email-jiapeng.chong@linux.alibaba.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>