UART: FIFO backend: Do not error out if other side disconnects Rx

The other side disconnecting its Rx side unexpectedly is not
necessarily an error.
So, instead of reporting an error in this case, let's
just print a message and exit.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>

src/HW_models/NHW_UART_backend_fifo.c

@@ -162,7 +162,7 @@ static void write_to_tx_fifo(struct ufifo_st_t *u_el, void *ptr, size_t size) {
     u_el->disconnected = true;
     if ((res == -1) && (errno == EPIPE)) {
       /* The other side disconnected unexpectedly, let's terminate */
-      bs_trace_error_time_line("UART: Other end disconnected unexpectedly, terminating\n");
+      bs_trace_exit_time_line("UART: Other end disconnected from its Rx FIFO, terminating\n");
     } else {
       bs_trace_error_time_line("UART: Unexpected error while writing (%i, %i) (or interrupted). "
                                "Terminating\n", res, errno);