ASoC: simple-card: Simplify code

The global DAI format is used only in the function
asoc_simple_card_parse_of(). So, move it from the private data
to the stack.

Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Reviewed-by: Xiubo Li <Li.Xiubo@freescale.com>
Signed-off-by: Mark Brown <broonie@linaro.org>