serial: 8250_early: Fix setup() error code

If parsing failed to decode a valid uart addr, return -ENODEV instead
of success. Although setup_earlycon() will detect the failure anyway
(because the write() method has not been set), that behavior is not
obvious and should not be relied on.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>