drm: Fix modifiers_property kernel doc

The member is called 'modifiers_property' instead of 'modifiers'. Adjust
the kernel docs to match.

Cc: dri-devel@lists.freedesktop.org
Cc: Ben Widawsky <ben@bwidawsk.net>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Cc: Daniel Stone <daniels@collabora.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170824191100.10949-11-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/drm/drm_mode_config.h

@@ -758,7 +758,7 @@ struct drm_mode_config {
 	bool allow_fb_modifiers;
 
 	/**
-	 * @modifiers: Plane property to list support modifier/format
+	 * @modifiers_property: Plane property to list support modifier/format
 	 * combination.
 	 */
 	struct drm_property *modifiers_property;