ASoC: simple-card: reduce naming prefix

Current simple-card is using asoc_simple_card_xxx() for
function / data naming. Because of this long prefix, it is easy to be
80 character over.
Let's reduce prefix from asoc_simple_card_xxx() to simple_xxx().
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>