spinlock: improve spin_is_locked() for recursive locks

spinlock: improve spin_is_locked() for recursive locks

Recursive locks know their current owner, and since we use the function
solely to determine whether a particular lock is being held by the
current CPU (which so far has been an imprecise check), make actually
check the owner for recusrively acquired locks.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Dario Faggioli <dario.faggioli@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Quan Xu <quan.xu@intel.com>
Acked-by: Tim Deegan <tim@xen.org>