hw/char/sifive_uart: Fix broken UART on big endian hosts

Casting a "uint32_t *" to a "uint8_t *" to get to the lowest 8-bit
part of the value does not work on big endian hosts. We've got to
take the proper detour through an 8-bit variable.

Fixes: 53c1557b23 ("hw/char: sifive_uart: Print uart characters async")
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20241104163504.305955-1-thuth@redhat.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

hw/char/sifive_uart.c

@@ -174,10 +174,11 @@ sifive_uart_write(void *opaque, hwaddr addr,
 {
     SiFiveUARTState *s = opaque;
     uint32_t value = val64;
+    uint8_t ch = value;
 
     switch (addr) {
     case SIFIVE_UART_TXFIFO:
-        sifive_uart_write_tx_fifo(s, (uint8_t *) &value, 1);
+        sifive_uart_write_tx_fifo(s, &ch, 1);
         return;
     case SIFIVE_UART_IE:
         s->ie = val64;