hw/intc/exynos4210_gic: Use more meaningful name for local variable

There are to SysBusDevice variables in exynos4210_gic_realize()
function: one for the device itself and second for arm_gic device.  Add
a prefix "gic" to the second one so it will be easier to understand the
code.

While at it, put local uninitialized 'i' variable at the end, next to
other uninitialized ones.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
