ASoC: rockchip: Revert "ASoC: rockchip: i2s: remove unused variables"

This reverts commit 5938448b

.

It turns out that the commit that made these variables unused is wrong
so we're about to revert it.  Bring back the variables in prepration.

Signed-off-by: John Keeping <john@metanate.com>
Signed-off-by: Mark Brown <broonie@kernel.org>