dt-bindings: rtc: sun6i-a31-rtc: Loosen the requirements on the clocks

The commit ec98a87509f4 ("rtc: sun6i: Make external 32k oscillator
optional") loosened the requirement of the clocks property, making it
optional. However, the binding still required it to be present.

Cc: Alexandre Belloni <[e-mail]>
Fixes: ec98a87509f4 ("rtc: sun6i: Make external 32k oscillator optional")
Signed-off-by: Maxime Ripard <[e-mail]>
Acked-by: Jernej Skrabec <[e-mail]>
Acked-by: Chen-Yu Tsai <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/devicetree/bindings/rtc/allwinner,sun6i-a31-rtc.yaml

···
   - compatible
   - reg
   - interrupts
-  - clocks
   - clock-output-names
 
 additionalProperties: false