ASoC: rsnd: use BRGCKR instead of SSICKR

Current register name of "SSICKR" was came from R-Car Gen1
which is very old style. It is called as "BRGCKR" on R-Car Gen2/Gen3.
Let's rename it

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