drm/amd/display/dc/core/dc_link: Fix a couple of function documentation issues

drm/amd/display/dc/core/dc_link: Fix a couple of function documentation issues

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_link.c:214: warning: Function parameter or member 'link' not described in 'dc_link_detect_sink'
 drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_link.c:350: warning: Function parameter or member 'link' not described in 'dc_link_is_dp_sink_present'
 drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_link.c:841: warning: Function parameter or member 'link' not described in 'dc_link_detect_helper'
 drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_link.c:841: warning: Function parameter or member 'reason' not described in 'dc_link_detect_helper'
 drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_link.c:3403: warning: Cannot understand  *****************************************************************************

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>