riscv: Fix sifive serial driver

Setup the port uartclk in sifive_serial_probe() so that the base baud
rate is correctly printed during device probe instead of always showing
"0".  I.e. the probe message is changed from

38000000.serial: ttySIF0 at MMIO 0x38000000 (irq = 1,
base_baud = 0) is a SiFive UART v0

to the correct:

38000000.serial: ttySIF0 at MMIO 0x38000000 (irq = 1,
base_baud = 115200) is a SiFive UART v0
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>
Acked-by: Palmer Dabbelt <palmerdabbelt@google.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

drivers/tty/serial/sifive.c

@@ -1000,6 +1000,7 @@ static int sifive_serial_probe(struct platform_device *pdev)
 	/* Set up clock divider */
 	ssp->clkin_rate = clk_get_rate(ssp->clk);
 	ssp->baud_rate = SIFIVE_DEFAULT_BAUD_RATE;
+	ssp->port.uartclk = ssp->baud_rate * 16;
 	__ssp_update_div(ssp);
 
 	platform_set_drvdata(pdev, ssp);