sh4: Fix serial line access for Linux kernels later than 3.2

With Linux kernel version 3.3 or later, qemu fails with the following message:

sh_serial: unsupported read from 0x18
  Aborted
Reported-and-analyzed-by: NRob Landley <rob@landley.net>
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

hw/char/sh_serial.c

@@ -248,11 +248,9 @@ static uint64_t sh_serial_read(void *opaque, hwaddr offs,
                     s->flags &= ~SH_SERIAL_FLAG_RDF;
             }
             break;
-#if 0
         case 0x18:
             ret = s->fcr;
             break;
-#endif
         case 0x1c:
             ret = s->rx_cnt;
             break;