usb: gadget: udc-core: fix the typo of udc state attribute

The name of udc state attribute file under sysfs is registered as
"state", while usb_gadget_set_state take it as "status" when it's
going to update. This patch fixes the typo.

Signed-off-by: Rong Wang <Rong.Wang@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Cc: <stable@kernel.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>