[GFS2] gfs2_set_flags double locking patch

traced the "umount hang due to spurious glock" issue that I was having
with gfs2meta. It's in the do_gfs2_set_flags function, which does a
gfs2_holder_init as well as a gfs2_glock_nq_init (increases ref count by
2 instead of 1).

Signed-off-by: Abhijith Das <adas@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>