ASoC: rt5640: Do not allow regmap to use bulk read-write operations

Debugging showed Realtek RT5642 doesn't support autoincrementing writes so
driver should set the use_single_rw flag for regmap.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
Cc: stable@vger.kernel.org