video: fm2fb: constify zorro_device_id

zorro_device_id are not supposed to change at runtime. All functions
working with zorro_device_id provided by <linux/zorro.h> work with
const zorro_device_id. So mark the non-const structs as const.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>