hw/intc: fix default registers value in exynos4210_combiner_read()

hw/intc: fix default registers value in exynos4210_combiner_read()

Clang static code analyzer show warning:
hw/intc/exynos4210_combiner.c:231:9: warning: Value stored to 'val' is never read
        val = s->reg_set[offset >> 2];

The default register return value should be return 'val'.

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Chen Qun <kuhn.chenqun@huawei.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20200827110311.164316-10-kuhn.chenqun@huawei.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>