dt-bindings: thermal: sun8i: Fix misplaced schema keyword in compatible strings

A compatible string 'enum' mistakenly has 'const: ' in the compatible
strings. Remove these.

Fixes: 0b28594d67a8 ("dt-bindings: thermal: Add YAML schema for sun8i-thermal driver bindings")
Cc: Vasily Khoruzhick <[e-mail]>
Cc: Yangtao Li <[e-mail]>
Cc: Zhang Rui <[e-mail]>
Cc: Daniel Lezcano <[e-mail]>
Cc: Amit Kucheria <[e-mail]>
Cc: Maxime Ripard <[e-mail]>
Cc: Chen-Yu Tsai <[e-mail]>
Cc: Jernej Skrabec <[e-mail]>
Cc: [e-mail]
Signed-off-by: Rob Herring <[e-mail]>
Acked-by: Maxime Ripard <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/devicetree/bindings/thermal/allwinner,sun8i-a83t-ths.yaml

···
         compatible:
           contains:
             enum:
-              - const: allwinner,sun8i-h3-ths
-              - const: allwinner,sun8i-r40-ths
-              - const: allwinner,sun50i-a64-ths
-              - const: allwinner,sun50i-a100-ths
-              - const: allwinner,sun50i-h5-ths
-              - const: allwinner,sun50i-h6-ths
+              - allwinner,sun8i-h3-ths
+              - allwinner,sun8i-r40-ths
+              - allwinner,sun50i-a64-ths
+              - allwinner,sun50i-a100-ths
+              - allwinner,sun50i-h5-ths
+              - allwinner,sun50i-h6-ths
 
     then:
       required: