drm/sun4i: Fix debug message in DE2

Debug message would print "Enabling" even when disabling plane.

Fix it.

Fixes: 9d75b8c0

 (drm/sun4i: add support for Allwinner DE2 mixers)

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171201060550.10392-5-jernej.skrabec@siol.net