tty: serial: cpm_uart: make use of for_each_node_by_type()

Instead of open-coding loop with of_find_node_by_type(), let's use canned
macro.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>