ACPI / ACPICA: Initialize the global lock spinlock as appropriate

Commit 9cd03144 (ACPI / ACPICA: Fix global lock acquisition) forgot to
initialize the spinlock it added.  Fix that.

Reported-and-tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Tested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>