hw/gpio/aspeed_gpio: Remove dead assignment

Fix warning reported by Clang static code analyzer:

  hw/gpio/aspeed_gpio.c:717:18: warning: Value stored to 'g_idx' during its initialization is never read
      int set_idx, g_idx = *group_idx;
                   ^~~~~   ~~~~~~~~~~

Reported-by: Clang Static Analyzer
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200422133152.16770-8-philmd@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

hw/gpio/aspeed_gpio.c

@@ -712,7 +712,7 @@ static void aspeed_gpio_write(void *opaque, hwaddr offset, uint64_t data,
 static int get_set_idx(AspeedGPIOState *s, const char *group, int *group_idx)
 {
     AspeedGPIOClass *agc = ASPEED_GPIO_GET_CLASS(s);
-    int set_idx, g_idx = *group_idx;
+    int set_idx, g_idx;
 
     for (set_idx = 0; set_idx < agc->nr_gpio_sets; set_idx++) {
         const GPIOSetProperties *set_props = &agc->props[set_idx];