ASoC: dt-bindings: Refine 'frame-master' and 'bitclock-master' type

'frame-master' and 'bitclock-master' are only a single phandle, so use
the more specific 'phandle' type definition instead.

Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Sameer Pujar <spujar@nvidia.com>
Link: https://lore.kernel.org/r/20201117013349.2458416-5-robh@kernel.org


Signed-off-by: Mark Brown <broonie@kernel.org>