drm/exynos: Add missing braces around sizeof in exynos_mixer.c

Fixes the following checkpatch warnings:
WARNING: sizeof filter_y_horiz_tap8 should be sizeof(filter_y_horiz_tap8)
WARNING: sizeof filter_y_vert_tap4 should be sizeof(filter_y_vert_tap4)
WARNING: sizeof filter_cr_horiz_tap4 should be sizeof(filter_cr_horiz_tap4)

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>