drm/gma500/oaktrail_crtc: Demote unworthy kernel-doc headers

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

 drivers/gpu/drm/gma500/oaktrail_crtc.c:184: warning: Function parameter or member 'limit' not described in 'mrst_lvds_find_best_pll'
 drivers/gpu/drm/gma500/oaktrail_crtc.c:184: warning: Function parameter or member 'crtc' not described in 'mrst_lvds_find_best_pll'
 drivers/gpu/drm/gma500/oaktrail_crtc.c:184: warning: Function parameter or member 'target' not described in 'mrst_lvds_find_best_pll'
 drivers/gpu/drm/gma500/oaktrail_crtc.c:184: warning: Function parameter or member 'refclk' not described in 'mrst_lvds_find_best_pll'
 drivers/gpu/drm/gma500/oaktrail_crtc.c:184: warning: Function parameter or member 'best_clock' not described in 'mrst_lvds_find_best_pll'
 drivers/gpu/drm/gma500/oaktrail_crtc.c:215: warning: Function parameter or member 'crtc' not described in 'oaktrail_crtc_dpms'
 drivers/gpu/drm/gma500/oaktrail_crtc.c:215: warning: Function parameter or member 'mode' not described in 'oaktrail_crtc_dpms'
 drivers/gpu/drm/gma500/oaktrail_crtc.c:345: warning: Function parameter or member 'dev' not described in 'oaktrail_panel_fitter_pipe'

Cc: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
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/20210115181601.3432599-21-lee.jones@linaro.org

drivers/gpu/drm/gma500/oaktrail_crtc.c

@@ -174,7 +174,7 @@ static bool mrst_sdvo_find_best_pll(const struct gma_limit_t *limit,
 	return min_error == 0;
 }
 
-/**
+/*
  * Returns a set of divisors for the desired target clock with the given refclk,
  * or FALSE.  Divisor values are the actual divisors for
  */
@@ -205,7 +205,7 @@ static bool mrst_lvds_find_best_pll(const struct gma_limit_t *limit,
 	return err != target;
 }
 
-/**
+/*
  * Sets the power management mode of the pipe and plane.
  *
  * This code should probably grow support for turning the cursor off and back
@@ -337,7 +337,7 @@ static void oaktrail_crtc_dpms(struct drm_crtc *crtc, int mode)
 	gma_power_end(dev);
 }
 
-/**
+/*
  * Return the pipe currently connected to the panel fitter,
  * or -1 if the panel fitter is not present or not in use
  */