staging/lustre: annotate lock/unlock in lov_stripe_lock / lov_stripe_unlock

Annotate the lock/unlock pair in lov_stripe_lock/lov_stripe_unlock to
avoid sparse warning about a context imbalance.
Part of the eudyptula challenge: http://eudyptula-challenge.org/



Signed-off-by: Mostyn Bramley-Moore <mbmcode@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>