CHROMIUM: drm: bridge/dw_hdmi: assign CD field to zero

CHROMIUM: drm: bridge/dw_hdmi: assign CD field to zero

When the color depth is 24 bits per pixel video, the CD
field in General Control Packet should be "Color Depth
not indicated", then the colordepth in register vp_pr_cd
& csc_scale should assign to zero.

Signed-off-by: Yakir Yang <ykk@rock-chips.com>
BUG=chrome-os-partner:38212
TEST=speedy board, Test with Agilent Technologies U4002A
     HDMI Protocal Analyzer

Change-Id: Ifd5767d339fdbff11e234ec0891c8f3df1dd66a5
Reviewed-on: https://chromium-review.googlesource.com/261850
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Tested-by: Yakir Yang <ykk@rock-chips.com>
Commit-Queue: Yakir Yang <ykk@rock-chips.com>
Signed-off-by: Zheng Yang <zhengyang@rock-chips.com>