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>

drivers/serial/serial_pl01x.c

@@ -117,7 +117,7 @@ static int pl01x_generic_setbrg(struct pl01x_regs *regs, enum pl01x_type type,
 			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;