dt-bindings: i2c: renesas,riic: Fix 'unevaluatedProperties' warnings

With 'unevaluatedProperties' support implemented, there's a number of
warnings when running dtbs_check:

arch/arm64/boot/dts/renesas/r9a07g043u11-smarc.dtb: i2c@10058000: Unevaluated properties are not allowed ('resets' was unexpected)
	From schema: Documentation/devicetree/bindings/i2c/renesas,riic.yaml

The main problem is that bindings schema marks resets as a required
property for RZ/G2L (and alike) SoC's but resets property is not part
of schema. So to fix this just add a resets property with maxItems
set to 1.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>