drm/dsc: fix DP_DSC_MAX_BPP_DELTA_* macro values

The macro values just don't match the specs. Fix them.

Fixes: 1482ec00

 ("drm: Add missing DP DSC extended capability definitions.")
Cc: Vinod Govindapillai <vinod.govindapillai@intel.com>
Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230406134615.1422509-2-jani.nikula@intel.com