drm: Fix warning when building docs for scdc_helper

Fixes:
../drivers/gpu/drm/drm_scdc_helper.c:203: ERROR: Unexpected indentation.
../drivers/gpu/drm/drm_scdc_helper.c:204: WARNING: Block quote ends without a blank line; unexpected unindent.

Changes in v2:
 - Property blockquote TMDS calculations so they look pretty (Daniel)
 - Remove duplicate documentation from the header file

Signed-off-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170720200921.36897-1-seanpaul@chromium.org