drm/sun4i: backend: Fix define typo

There was a typo in the width spelling of the (unused)
SUN4I_BACKEND_IYUVLINEWITDTH_REG macro. Fix it.

Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/6b2e872b611b733a98a38902a2197b70c725e0b9.1516617243.git-series.maxime.ripard@free-electrons.com