serial: 8250_bcm2835aux: Suppress register_port error on -EPROBE_DEFER

Suppress a gratuitous error message if serial8250_register_8250_port()
returns -EPROBE_DEFER.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Matthias Brugger <mbrugger@suse.com>
Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Link: https://lore.kernel.org/r/6aea0eacf3bfa73fe2d81082cc723265413410c8.1579175223.git.lukas@wunner.de


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>