slavio_misc: avoid structure holes spotted by pahole

slavio_misc: avoid structure holes spotted by pahole

Report from pahole on amd64 host:
struct MiscState {
	SysBusDevice               busdev;               /*     0  5648 */
	/* --- cacheline 88 boundary (5632 bytes) was 16 bytes ago --- */
	qemu_irq                   irq;                  /*  5648     8 */
	uint32_t                   dummy;                /*  5656     4 */
	uint8_t                    config;               /*  5660     1 */
	uint8_t                    aux1;                 /*  5661     1 */
	uint8_t                    aux2;                 /*  5662     1 */
	uint8_t                    diag;                 /*  5663     1 */
	uint8_t                    mctrl;                /*  5664     1 */
	uint8_t                    sysctrl;              /*  5665     1 */
	uint16_t                   leds;                 /*  5666     2 */

	/* XXX 4 bytes hole, try to pack */

	qemu_irq                   fdc_tc;               /*  5672     8 */

	/* size: 5680, cachelines: 89 */
	/* sum members: 5676, holes: 1, sum holes: 4 */
	/* last cacheline: 48 bytes */
};	/* definitions: 1 */

Fix by rearranging the structure to avoid padding.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>