acer-wmi: avoid the warning of 'devices' may be used uninitialized

Fengguang Wu run kernel build test to platform-drivers-x86/linux-next git tree
on x86_64 architecture and found a warning that was introduced by
727651bf738b6b917335025d09323d0962eda114 commit:

drivers/platform/x86/acer-wmi.c: In function ‘WMID_set_capabilities’:
drivers/platform/x86/acer-wmi.c:1211: warning: ‘devices’ may be used
uninitialized in this function

This patch fixes the above warning message.

Cc: Carlos Corbacho <carlos@strangeworlds.co.uk>
Cc: Matthew Garrett <mjg@redhat.com>
Cc: Dmitry Torokhov <dtor@mail.ru>
Cc: Corentin Chary <corentincj@iksaif.net>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Lee, Chun-Yi <jlee@suse.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>