ASoC: rcar: some dubious one-bit signed bitfields

Because these are signed they can either be 0 or -1 instead of 0 and 1
as intended.  It doesn't cause a problem from what I can see, but it's
dangerous and Sparse complains:

	sound/soc/sh/rcar/rsnd.h:177:25:
		error: dubious one-bit signed bitfield

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mark Brown <broonie@linaro.org>