drm/amd/display: Add missing do_mccs parameter description

drm/amd/display: Add missing do_mccs parameter description

Add missing description for do_mccs parameter in
amdgpu_dm_update_freesync_caps.

Fixes the below with gcc W=1:
../display/amdgpu_dm/amdgpu_dm.c:13269 function parameter 'do_mccs' not described in 'amdgpu_dm_update_freesync_caps'

Fixes: 8dc88c6a5948 ("drm/amd/display: Avoid to do MCCS transaction if unnecessary")
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Wayne Lin <Wayne.Lin@amd.com>
Cc: Roman Li <roman.li@amd.com>
Cc: Alex Hung <alex.hung@amd.com>
Cc: Tom Chung <chiahsuan.chung@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>