examples: uart: Fix port configuration
examples: uart: Fix port configuration

mraa_uart_settings retrieves the settings, it does not apply them.

Signed-off-by: Jan Kiszka <a5b45c9af271d077f30d36aa7d9b988eed9d56eb@siemens.com>

g-vidal/mraa,g-vidal/mraa,g-vidal/mraa,g-vidal/mraa,g-vidal/mraa