ASoC: rt286: Fix sync function

We try to write index registers into cache when we write an index
register, but we change the reg value before updating the cache.
As a result, the cache is never be updated. This patch will fix
this issue.

Signed-off-by: Bard Liao <bardliao@realtek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org