drm: Tweak drm_encoder_helper_funcs.enable kerneldoc

I copied the kerneldoc for encoder_funcs.atomic_enable from encoder_funcs.enable
in a recent patch [1]. Sam rightly pointed out in the review that "for symmetry
with" text is awkward [2]. So here's a patch to fix up the source of the awkward
language.

[1] https://patchwork.freedesktop.org/patch/msgid/20190611160844.257498-2-sean@poorly.run
[2] https://patchwork.freedesktop.org/patch/msgid/20190611185352.GA16305@ravnborg.orgSuggested-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190612150038.194843-1-sean@poorly.run

include/drm/drm_modeset_helper_vtables.h

@@ -719,11 +719,11 @@ struct drm_encoder_helper_funcs {
 	 * hooks and call them from CRTC's callback by looping over all encoders
 	 * connected to it using for_each_encoder_on_crtc().
 	 *
-	 * This hook is used only by atomic helpers, for symmetry with @disable.
-	 * Atomic drivers don't need to implement it if there's no need to
-	 * enable anything at the encoder level. To ensure that runtime PM handling
-	 * (using either DPMS or the new "ACTIVE" property) works
-	 * @enable must be the inverse of @disable for atomic drivers.
+	 * This hook is only used by atomic helpers, it is the opposite of
+	 * @disable. Atomic drivers don't need to implement it if there's no
+	 * need to enable anything at the encoder level. To ensure that
+	 * runtime PM handling (using either DPMS or the new "ACTIVE" property)
+	 * works @enable must be the inverse of @disable for atomic drivers.
 	 */
 	void (*enable)(struct drm_encoder *encoder);