drm: drm_mode_config.h: delete duplicated words in comments

Drop doubled word "is" in several comments.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200715052349.23319-4-rdunlap@infradead.org

include/drm/drm_mode_config.h

@@ -603,22 +603,22 @@ struct drm_mode_config {
 	struct drm_property *prop_src_h;
 	/**
 	 * @prop_crtc_x: Default atomic plane property for the plane destination
-	 * position in the &drm_crtc is is being shown on.
+	 * position in the &drm_crtc is being shown on.
 	 */
 	struct drm_property *prop_crtc_x;
 	/**
 	 * @prop_crtc_y: Default atomic plane property for the plane destination
-	 * position in the &drm_crtc is is being shown on.
+	 * position in the &drm_crtc is being shown on.
 	 */
 	struct drm_property *prop_crtc_y;
 	/**
 	 * @prop_crtc_w: Default atomic plane property for the plane destination
-	 * position in the &drm_crtc is is being shown on.
+	 * position in the &drm_crtc is being shown on.
 	 */
 	struct drm_property *prop_crtc_w;
 	/**
 	 * @prop_crtc_h: Default atomic plane property for the plane destination
-	 * position in the &drm_crtc is is being shown on.
+	 * position in the &drm_crtc is being shown on.
 	 */
 	struct drm_property *prop_crtc_h;
 	/**