md: use mddev_suspend/resume instead of ->quiesce()

commit 9e1cc0a54556a6c63dc0cfb7cd7d60d43337bba6 upstream.

mddev_suspend() is a more general interface than
calling ->quiesce() and is so more extensible.  A
future patch will make use of this.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jack Wang <jinpu.wang@profitbricks.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>