ASoC: rsnd: tidyup registering method for rsnd_kctrl_new()

Current rsnd dvc.c is using flags to avoid duplicating register for
MIXer case. OTOH, commit e894efef ("ASoC: core: add support to card
rebind") allows to rebind sound card without rebinding all drivers.

Because of above patch and dvc.c flags, it can't re-register kctrl if
only sound card was rebinded, because dvc is keeping old flags.
(Of course it will be no problem if rsnd driver also be rebinded,
but it is not purpose of above patch).

This patch checks current card registered kctrl when registering.
In MIXer case, it can avoid duplicate register if card already has same
kctrl. In rebind case, it can re-register kctrl because card registered
kctl had been removed when unbinding.

This patch is updated version of commit b918f1bc

 ("ASoC: rsnd: DVC
kctrl sets once")

Reported-by: Nguyen Viet Dung <dung.nguyen.aj@renesas.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Nguyen Viet Dung <dung.nguyen.aj@renesas.com>
Cc: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>