We kzalloc.

Cc: Keith Packard <keithp@keithp.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190228144910.26488-4-daniel.vetter@ffwll.ch