drm/print: Fix DRM_DEBUG_DP macro

This isn't supposed to take dev as an argument, I guess no one noticed!

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180718215716.5784-1-lyude@redhat.com