hw/display/qxl: Remove unneeded variable assignment

Fix warning reported by Clang static code analyzer:

  hw/display/qxl.c:1634:14: warning: Value stored to 'orig_io_port' during its initialization is never read
      uint32_t orig_io_port = io_port;
               ^~~~~~~~~~~~   ~~~~~~~

Reported-by: Clang Static Analyzer
Signed-off-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Message-Id: <20200215161557.4077-3-philmd@redhat.com>
Signed-off-by: NLaurent Vivier <laurent@vivier.eu>

hw/display/qxl.c

@@ -1631,7 +1631,7 @@ static void ioport_write(void *opaque, hwaddr addr,
     PCIQXLDevice *d = opaque;
     uint32_t io_port = addr;
     qxl_async_io async = QXL_SYNC;
-    uint32_t orig_io_port = io_port;
+    uint32_t orig_io_port;
 
     if (d->guest_bug && io_port != QXL_IO_RESET) {
         return;