xtensa: use newer __SPIN_LOCK_UNLOCKED macro

SPIN_LOCK_UNLOCKED() breaks lockdep and is deprecated.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chris Zankel <chris@zankel.net>