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>