ASoC: rt5677: set PLL_CTRL2 non-volatile

There is a status bit on RT5677_PLL1_CTRL2 and RT5677_PLL2_CTRL2.
That's why those registers are set volatile. However, the status
bit is currently not used by codec driver. So, it should be no
problem if we set them non-volatile.
The purpose of setting them non-volatile is to restore the setting
after a syspend/resume cycle.

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