fixed the function header (#7674)

* fixed the function header

* fixed function name and paramaters

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Co-authored-by: Jan Procházka <90197375+P-R-O-C-H-Y@users.noreply.github.com>

docs/source/api/sigmadelta.rst

@@ -28,7 +28,7 @@ This function is used to setup the SigmaDelta channel frequency and resolution.
 
 .. code-block:: arduino
 
-    double ledcSetup(uint8_t channel, double freq, uint8_t resolution_bits);
+    uint32_t sigmaDeltaSetup(uint8_t pin, uint8_t channel, uint32_t freq);
 
 * ``pin`` select GPIO pin.
 * ``channel`` select SigmaDelta channel.