drm/gma500/psb_intel_sdvo: Demote kernel-doc abuses

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

 drivers/gpu/drm/gma500/psb_intel_sdvo.c:230: warning: Function parameter or member 'psb_intel_sdvo' not described in 'psb_intel_sdvo_write_sdvox'
 drivers/gpu/drm/gma500/psb_intel_sdvo.c:230: warning: Function parameter or member 'val' not described in 'psb_intel_sdvo_write_sdvox'
 drivers/gpu/drm/gma500/psb_intel_sdvo.c:598: warning: Function parameter or member 'psb_intel_sdvo' not described in 'psb_intel_sdvo_get_trained_inputs'
 drivers/gpu/drm/gma500/psb_intel_sdvo.c:598: warning: Function parameter or member 'input_1' not described in 'psb_intel_sdvo_get_trained_inputs'
 drivers/gpu/drm/gma500/psb_intel_sdvo.c:598: warning: Function parameter or member 'input_2' not described in 'psb_intel_sdvo_get_trained_inputs'
 drivers/gpu/drm/gma500/psb_intel_sdvo.c:1831: warning: Function parameter or member 'dev_priv' not described in 'psb_intel_sdvo_select_ddc_bus'
 drivers/gpu/drm/gma500/psb_intel_sdvo.c:1831: warning: Function parameter or member 'sdvo' not described in 'psb_intel_sdvo_select_ddc_bus'
 drivers/gpu/drm/gma500/psb_intel_sdvo.c:1831: warning: Function parameter or member 'reg' not described in 'psb_intel_sdvo_select_ddc_bus'

Cc: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Jesse Barnes <jesse.barnes@intel.com>
Cc: Eric Anholt <eric@anholt.net>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210115181601.3432599-12-lee.jones@linaro.org