Since the previous commit, function gfs2_quota_sync() will not cause the
sync generation to creep forward by one every time the function is
called; this helps keep things a but more tidy.  We also don't care that
this function allocates a page of memory every time it is called, so no
good reason for keeping qd_changed() anymore, which just duplicates
qd_grab_sync().

This reverts commit 06aa6fd3.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>