drm/dp: Describe target_rr_divider in struct drm_dp_as_sdp

drm/dp: Describe target_rr_divider in struct drm_dp_as_sdp

Describe newly added parameter target_rr_divider in struct
drm_dp_as_sdp.

-v2:
Remove extra line from commit message.(Lucas)

-v3:
Rebase.

Fixes: a20c6d954d75 ("drm/dp: Add refresh rate divider to struct representing AS SDP")
Cc: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
Cc: Arun R Murthy <arun.r.murthy@intel.com>
Cc: Suraj Kandpal <suraj.kandpal@intel.com>
Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240715162514.2836421-1-mitulkumar.ajitkumar.golani@intel.com