drm: fix typo in margin connector properties docs

This was pointed out by Ville and Pekka in their replies, but
forgot to apply the change properly before pushing. Sorry for
the noise!
Signed-off-by: Simon Ser <contact@emersion.fr>
Fixes: 409f07d3 ("drm: document connector margin properties")
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Pekka Paalanen <pekka.paalanen@collabora.com>
Cc: Maxime Ripard <maxime@cerno.tech>
Cc: Dave Stevenson <dave.stevenson@raspberrypi.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230305103503.42619-1-contact@emersion.fr

drivers/gpu/drm/drm_connector.c

@@ -1452,7 +1452,7 @@ static const struct drm_prop_enum_list dp_colorspaces[] = {
  *
  * left margin, right margin, top margin, bottom margin:
  *	Add margins to the connector's viewport. This is typically used to
- *	mitigate underscan on TVs.
+ *	mitigate overscan on TVs.
  *
  *	The value is the size in pixels of the black border which will be
  *	added. The attached CRTC's content will be scaled to fill the whole