dt-bindings: arm: fsl: Fix copy-paste error in comment

The imx6dl-yapp4-draco board is actually based on the i.MX6Solo SoC.
Fix the comment to match reality.

Fixes: 24ef3b6e ("dt-bindings: arm: Add Y Soft IOTA Draco, Hydra and Ursa boards")
Signed-off-by: Michal Vokáč <michal.vokac@ysoft.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>