sgi-xp: Replace spin_is_locked() with lockdep

lockdep_assert_held() is better suited to checking locking requirements,
since it won't get confused when someone else holds the lock. This is
also a step towards possibly removing spin_is_locked().

Signed-off-by: Lance Roy <ldr709@gmail.com>
Cc: Cliff Whickman <cpw@sgi.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Acked-by: Robin Holt <robinmholt@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>