ASoC: rsnd: care default case on rsnd_ssiu_busif_err_status_clear()

commit cfb7b8bf

 ("ASoC: rsnd: tidyup
rsnd_ssiu_busif_err_status_clear()") merged duplicate code, but it didn't
care about default case, and causes smatch warnings.

smatch warnings:
sound/soc/sh/rcar/ssiu.c:112 rsnd_ssiu_busif_err_status_clear() \
	error: uninitialized symbol 'offset'.
sound/soc/sh/rcar/ssiu.c:114 rsnd_ssiu_busif_err_status_clear() \
	error: uninitialized symbol 'shift'.

This patch cares it.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87r15rgn6p.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>