platform/x86: xiaomi-wmi: Drop unnecessary NULL checks

The WMI driver core already makes sure that:

- a valid WMI device is passed to each callback
- the notify() callback runs after the probe() callback succeeds

Remove the unnecessary NULL checks.

Compile-tested only.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20240402143059.8456-3-W_Armin@gmx.de


Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>