drm/encoder: Fix possible_crtcs documentation

Similar to possible_clones, we don't actually use possible_crtcs until
the driver is registered with userspace. So, fix the documentation to
indicate this.
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190913222704.8241-3-lyude@redhat.comReviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/drm/drm_encoder.h

@@ -140,7 +140,7 @@ struct drm_encoder {
 	 * @possible_crtcs: Bitmask of potential CRTC bindings, using
 	 * drm_crtc_index() as the index into the bitfield. The driver must set
 	 * the bits for all &drm_crtc objects this encoder can be connected to
-	 * before calling drm_encoder_init().
+	 * before calling drm_dev_register().
 	 *
 	 * In reality almost every driver gets this wrong.
 	 *