GFS2: Don't bother trying to add rgrps to the lru list

This patch removes a call to gfs2_glock_add_to_lru from function
gfs2_clear_rgrpd. The call is just a waste of time because as soon
as it adds it to the lru_list, the call to gfs2_glock_put takes it
back off again.

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