tools: ffs-aio-example: convert to new descriptor format

Since commit [ac8dde11

: “Add flags to descriptors block”] functionfs
supports a new descriptor format, so we update example application
to make it using recomended version of descriptors.

Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Robert Baldyga <r.baldyga@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>