drm/exynos: dp: Lower level of EDID read success message

Don't pollute the dmesg with EDID read success message as an error.
Printing as debug should be fine.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>