drm/bridge: Centralize error message when bridge attach fails

Being informed of a failure to attach a bridge is useful, and many
drivers prints an error message in that case. Move the message to
drm_bridge_attach() to avoid code duplication.

Suggested-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Jyri Sarha <jyri.sarha@iki.fi>