gfs2: Don't set GLF_LOCK in gfs2_dispose_glock_lru

In gfs2_dispose_glock_lru(), we want to skip glocks which are in the
process of transitioning state (as indicated by the set GLF_LOCK flag),
but we we don't need to set that flag for requesting a state transition.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>