gfs2: move qdsb_put and reduce redundancy

This patch looks more invasive than it is. It simply moves function
qdsb_put before qd_unlock, then changes qd_unlock to call it rather than
open coding it. Again, this reduces redundancy.

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