drm/sun4i: Fix sparse warnings

drm/sun4i/sun4i_tv.c:181:21: warning: symbol 'ntsc_video_levels' was not declared. Should it be static?
drm/sun4i/sun4i_tv.c:185:21: warning: symbol 'pal_video_levels' was not declared. Should it be static?
drm/sun4i/sun4i_tv.c:189:21: warning: symbol 'ntsc_burst_levels' was not declared. Should it be static?
drm/sun4i/sun4i_tv.c:193:21: warning: symbol 'pal_burst_levels' was not declared. Should it be static?
drm/sun4i/sun4i_tv.c:197:20: warning: symbol 'ntsc_color_gains' was not declared. Should it be static?
drm/sun4i/sun4i_tv.c:201:20: warning: symbol 'pal_color_gains' was not declared. Should it be static?
drm/sun4i/sun4i_tv.c:205:26: warning: symbol 'ntsc_resync_parameters' was not declared. Should it be static?
drm/sun4i/sun4i_tv.c:209:26: warning: symbol 'pal_resync_parameters' was not declared. Should it be static?
drm/sun4i/sun4i_tv.c:213:16: warning: symbol 'tv_modes' was not declared. Should it be static?

Cc: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>