platform/x86: xiaomi-wmi: Fix race condition when reporting key events

Multiple WMI events can be received concurrently, so multiple instances
of xiaomi_wmi_notify() can be active at the same time. Since the input
device is shared between those handlers, the key input sequence can be
disturbed.

Fix this by protecting the key input sequence with a mutex.

Compile-tested only.

Fixes: edb73f4f ("platform/x86: wmi: add Xiaomi WMI key driver")
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20240402143059.8456-2-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>