greybus: uart: Update line coding settings only when needed

The check for line coding changed should use memcmp and not memcpy.

Testing done: trivial

Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Axel Haslam <ahaslam@baylibre.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>