Fix build warnings from drivers/mtd/redboot.c due to
use of `unsigned long` in `struct fis_image_desc` for
fields being passed to swab32s() which expects __u32 *

Change the entries to uint32_t to make them compatible
with the swab32s() function
Signed-off-by: NBen Dooks <ben-linux@fluff.org>
Signed-off-by: NDavid Woodhouse <dwmw2@infradead.org>