ASoC: da7213: Correct units description of dmic-clkrate

Description previously stated MHz whereas the resolution is in Hz.
This has now has been updated to align with reality.
Signed-off-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/da7213.txt

@@ -18,7 +18,7 @@ Optional properties:
 	["lrise_rfall", "lfall_rrise"]
 - dlg,dmic-samplephase : When to sample audio from DMIC.
 	["on_clkedge", "between_clkedge"]
-- dlg,dmic-clkrate : DMIC clock frequency (MHz).
+- dlg,dmic-clkrate : DMIC clock frequency (Hz).
 	[<1500000>, <3000000>]
 
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