platform/x86: asus-wmi: Delete impossible condition

The "asus->throttle_thermal_policy_mode" variable is a u8 so it can't
be negative.  And we always verify that the value is valid before
setting the policy mode so there is no need to check again here.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20210824113654.GA31143@kili


Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>