A final test with unmodified code has shown that a delay of 150ms

is not giving us a 100% success rate. Bump the delay to 200ms as
that seems to do the trick.

Note that during testing the delay was added to uart_bus_attach()
in uart_core.c. While having the delay in a different place can
change the behaviour, it was not expected. Having to bump the
delay with another 50ms could therefore be an indication that
the problem can not be solved with delays.

Reported by: kevlo@
Tested by: kevlo@

sys/dev/uart/uart_dev_ns8250.c

@@ -465,7 +465,7 @@ ns8250_bus_attach(struct uart_softc *sc)
 	 * accidental manner as before. More analysis is warranted, but
 	 * at least now we fixed a known regression.
 	 */
-	DELAY(150);
+	DELAY(200);
 	return (0);
 }