Checking both is one too much, so wrap a WARN_ON around it to stope
the copypasta.

Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Brian Starkey <brian.starkey@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191213172612.1514842-2-daniel.vetter@ffwll.ch