mfd: wm8994: Remove check for active audio in runtime suspend

Since enabling VMID takes a runtime PM reference there is no need to
suppress suspend when doing a runtime suspend. Similarly the digital
inputs and outputs are DAPM widgets and therefore the ASoC core will
be holding a reference for them.

This used to be required when integration with system suspend was being
bodged.

Signed-off-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>