Fix a bug with PL010s running at 19200 baud

I don't have the hardware test this, but it is almost certainly a typo
in the code dating back to at least 2004.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
diff --git a/drivers/serial/serial_pl01x.c b/drivers/serial/serial_pl01x.c
index a49134a..941b424 100644
--- a/drivers/serial/serial_pl01x.c
+++ b/drivers/serial/serial_pl01x.c
@@ -117,7 +117,7 @@
 			divisor = UART_PL010_BAUD_9600;
 			break;
 		case 19200:
-			divisor = UART_PL010_BAUD_9600;
+			divisor = UART_PL010_BAUD_19200;
 			break;
 		case 38400:
 			divisor = UART_PL010_BAUD_38400;