hw/intc/exynos4210_gic: Constify array of combiner interrupts

The static array of interrupt combiner mappings is not modified so it
can be made const for code safeness.
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/intc/exynos4210_gic.c

@@ -116,7 +116,7 @@ enum ExtInt {
  * which is INTG16 in Internal Interrupt Combiner.
  */
 
-static uint32_t
+static const uint32_t
 combiner_grp_to_gic_id[64-EXYNOS4210_MAX_EXT_COMBINER_OUT_IRQ][8] = {
     /* int combiner groups 16-19 */
     { }, { }, { }, { },