ieee1394: ieee1394_core.c: use DEFINE_SPINLOCK for spinlock definition

drivers/ieee1394/ieee1394_core.c: Define spinlock using
DEFINE_SPINLOCK instead of assignment to SPIN_LOCK_UNLOCKED

Signed-off-by: Matthias Kaehlcke <matthias.kaehlcke@gmail.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>