dt-bindings: rng: add clock detection error for stm32

Add optional property to enable the clock detection error
on rng block. It is used to allow slow clock source which
give correct entropy for rng.
Signed-off-by: NLionel Debieve <lionel.debieve@st.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

Documentation/devicetree/bindings/rng/st,stm32-rng.txt

@@ -13,6 +13,7 @@ Required properties:
 
 Optional properties:
 - resets : The reset to properly start RNG
+- clock-error-detect : Enable the clock detection management
 
 Example: