dt-bindings: sound: wm8994: Correct required supplies based on actual implementaion

The required supplies in bindings were actually not matching
implementation making the bindings incorrect and misleading.  The Linux
kernel driver requires all supplies to be present.  Also for wlf,wm8994
uses just DBVDD-supply instead of DBVDDn-supply (n: <1,3>).

Reported-by: Jonathan Bakker <xc-racer2@live.ca>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200501133534.6706-1-krzk@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>