drm/rockchip: cdn-dp: fix cdn-dp complie warning

fix warning:

drivers/gpu/drm/rockchip/cdn-dp-reg.c:632:24: warning:
  'val[1]' may be used uninitialized in this function [-Wmaybe-uninitialized]
  msa_misc = 2 * val[0] + 32 * val[1] +

Signed-off-by: Mark Yao <mark.yao@rock-chips.com>