ASoC: rcar: remove rsnd_kctrl_remove()

Current rcar driver is trying to remove kctrl when remove time.
But, 1) rcar driver can't/shouldn't remove before removing sound
card driver, 2) sound card driver will call snd_ctl_dev_free()
and removes all kctrls by snd_ctl_remove().
Thus, rsnd_kctrl_remove() is not necessary. Current implementation
will get Oops when removing rcar driver after sound card.
This patch fix this issue.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>