USB: serial: use dev_err_console in custom write paths

Use dev_err_console in write paths for devices which can be used as a
console but do not use the generic write implementation.

Compile-only tested.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>