ASoC: wm8994: Prevent access to invalid VU register bits on WM1811

The ADC2 and DAC2 are not available on WM1811 device. This patch moves
the ADC2, DAC2 VU bitfields to a separate array so we can skip accessing
them and avoid unreadable register access on WM1811.

This allows to get rid of warnings during boot like:
wm8994-codec: ASoC: error at soc_component_read_no_lock on wm8994-codec: -5

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Link: https://lore.kernel.org/r/20200804141043.11425-1-s.nawrocki@samsung.com
Signed-off-by: Mark Brown <broonie@kernel.org>