usb: gadget: functionfs: fix typo in the enum variable

Since “cancelled” is spelled with two “l”s, rename FFS_SETUP_CANCELED
to FFS_SETUP_CANCELLED.

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