drm/core: Use proper debugging macro

Use drm_dbg_kms() instead of DRM_DEBUG_KMS.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200331155308.6345-2-andrzej.p@collabora.com